diff --git a/pom.xml b/pom.xml
index c0adb07..bfbffce 100644
--- a/pom.xml
+++ b/pom.xml
@@ -65,7 +65,7 @@
         <dependency>
             <groupId>org.spigotmc</groupId>
             <artifactId>spigot-api</artifactId>
-            <version>1.21.3-R0.1-SNAPSHOT</version>
+            <version>1.21.4-R0.1-SNAPSHOT</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
diff --git a/src/main/java/net/knarcraft/blacksmith/command/CostCommand.java b/src/main/java/net/knarcraft/blacksmith/command/CostCommand.java
index d372438..a372483 100644
--- a/src/main/java/net/knarcraft/blacksmith/command/CostCommand.java
+++ b/src/main/java/net/knarcraft/blacksmith/command/CostCommand.java
@@ -3,16 +3,31 @@ package net.knarcraft.blacksmith.command;
 import net.knarcraft.blacksmith.BlacksmithPlugin;
 import net.knarcraft.blacksmith.container.ActionCost;
 import net.knarcraft.blacksmith.formatting.BlacksmithTranslatableMessage;
+import net.knarcraft.blacksmith.property.CostType;
+import org.bukkit.Bukkit;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandSender;
 import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.permissions.Permission;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.StringJoiner;
 
 public class CostCommand implements TabExecutor {
 
+    private static List<String> plugins;
+    private static Map<String, List<String>> permissions;
+
     @Override
     public boolean onCommand(@NotNull CommandSender commandSender, @NotNull Command command, @NotNull String s, @NotNull String[] arguments) {
         //TODO: Whenever a cost is specified (not for the per-material and per-enchantment costs), allow either a simple
@@ -20,33 +35,27 @@ public class CostCommand implements TabExecutor {
         // TODO: The command should look like "blacksmithEdit <option> <simple|advanced> <double|economy|item|permission|exp>
         //  <double|blank/null|comma-separated-string|integer>"
 
+        if (!(commandSender instanceof Player player)) {
+            commandSender.sendMessage("This command can only be used by players");
+            return false;
+        }
+
         //TODO: Check arguments size
         if (arguments.length < 2) {
             return false;
         }
 
+        ActionCost oldCost = new ActionCost(0, 0, null, Set.of());
+
         ActionCost actionCost;
 
-        switch (arguments[0]) {
+        switch (arguments[0].toLowerCase()) {
             case "simple":
                 // TODO: Do something with the cost
                 double cost = parseSimpleCost(commandSender, arguments[1]);
                 break;
             case "advanced":
-                switch (arguments[1]) {
-                    case "economy":
-                        // TODO: Expect the next argument to be the cost
-                        break;
-                    case "item":
-                        // TODO: The next argument would either be "null" to clear the value, or "mainHand" to use the item in the player's main hand
-                        break;
-                    case "permission":
-                        // TODO: The next argument will be a comma-separated list of permissions
-                        break;
-                    case "exp":
-                        // TODO: Expect the next argument to be an integer
-                        break;
-                }
+                actionCost = modifyActionCost(arguments, oldCost, player);
                 break;
             default:
                 return false;
@@ -56,10 +65,129 @@ public class CostCommand implements TabExecutor {
 
     @Override
     public @Nullable List<String> onTabComplete(@NotNull CommandSender commandSender, @NotNull Command command,
-                                                @NotNull String s, @NotNull String[] strings) {
+                                                @NotNull String s, @NotNull String[] arguments) {
+        if (plugins == null) {
+            loadAvailablePermissions();
+        }
+
+        if (arguments.length == 1) {
+            return List.of("simple", "advanced");
+        } else if (arguments.length == 2) {
+            if (arguments[0].equalsIgnoreCase("simple")) {
+                return List.of("");
+            } else {
+                return List.of("add", "set", "clear");
+            }
+        } else if (arguments.length == 3) {
+            if (arguments[0].equalsIgnoreCase("simple")) {
+                return List.of("");
+            } else {
+                return List.of("economy", "item", "exp", "permission");
+            }
+        } else if (arguments.length == 4) {
+            CostType costType = CostType.parse(arguments[2]);
+            if (costType == null) {
+                return null;
+            }
+            return switch (costType) {
+                case PERMISSION -> tabCompletePermission(arguments[3]);
+                case ECONOMY -> List.of("0.5", "1", "10");
+                case EXP -> List.of("1, 5, 10");
+                case ITEM -> List.of();
+            };
+        }
         return List.of();
     }
 
+    /**
+     * Modifies the cost of an action
+     *
+     * @param arguments <p>The arguments given by a player</p>
+     * @param oldCost   <p>The previous cost of the action</p>
+     * @param player    <p>The player attempting to alter the action cost</p>
+     * @return <p>The modified action cost, or null if something went wrong</p>
+     */
+    private ActionCost modifyActionCost(@NotNull String[] arguments, @NotNull ActionCost oldCost, @NotNull Player player) {
+        CostType costType;
+        if (arguments.length > 2) {
+            costType = CostType.parse(arguments[2]);
+        } else {
+            costType = null;
+        }
+
+        switch (arguments[1].toLowerCase()) {
+            case "add":
+                if (costType == null) {
+                    player.sendMessage("Invalid cost type specified!");
+                    return null;
+                }
+                return parseCost(costType, Arrays.copyOfRange(arguments, 2, arguments.length), oldCost, player);
+            case "clear":
+                // Clears one or all fields of a cost
+                if (costType == null) {
+                    return new ActionCost(0, 0, null, Set.of());
+                } else {
+                    return switch (costType) {
+                        case EXP -> oldCost.changeExpCost(0);
+                        case ITEM -> oldCost.changeItemCost(null);
+                        case ECONOMY -> oldCost.changeMonetaryCost(0);
+                        case PERMISSION -> oldCost.changePermissionCost(Set.of());
+                    };
+                }
+            case "set":
+                if (costType == null) {
+                    player.sendMessage("Invalid cost type specified!");
+                    return null;
+                }
+                return parseCost(costType, Arrays.copyOfRange(arguments, 2, arguments.length),
+                        new ActionCost(0, 0, null, Set.of()), player);
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * Parses an advanced action cost
+     *
+     * @param costType  <p>The type of cost to parse</p>
+     * @param arguments <p>The arguments given by the player</p>
+     * @param oldCost   <p>The old cost to modify</p>
+     * @param player    <p>The player changing the value</p>
+     * @return <p>The new action cost, or null if the process failed.</p>
+     */
+    @Nullable
+    private ActionCost parseCost(@NotNull CostType costType, @NotNull String[] arguments, @NotNull ActionCost oldCost,
+                                 @NotNull Player player) {
+        switch (costType) {
+            case ECONOMY:
+                double economyCost = Double.parseDouble(arguments[0]);
+                if (economyCost < 0) {
+                    player.sendMessage("Cost cannot be negative!");
+                    return null;
+                }
+                return oldCost.changeMonetaryCost(economyCost);
+            case ITEM:
+                ItemStack itemCost = player.getInventory().getItemInMainHand();
+                if (itemCost.getType().isAir()) {
+                    player.sendMessage("You have no item in your main hand");
+                    return null;
+                }
+                return oldCost.changeItemCost(itemCost);
+            case PERMISSION:
+                Set<String> permissionSet = new HashSet<>(Arrays.asList(arguments[0].split(",")));
+                return oldCost.changePermissionCost(permissionSet);
+            case EXP:
+                int expCost = Integer.parseInt(arguments[0]);
+                if (expCost < 0) {
+                    player.sendMessage("Exp cost cannot be negative!");
+                    return null;
+                }
+                return oldCost.changeExpCost(expCost);
+            default:
+                return null;
+        }
+    }
+
     /**
      * Parses a simple double cost
      *
@@ -83,4 +211,103 @@ public class CostCommand implements TabExecutor {
         }
     }
 
+    /**
+     * Gets the tab complete value for the permission typed
+     *
+     * @param typedNode <p>The full permission node typed by the player</p>
+     * @return <p>All known valid auto-complete options</p>
+     */
+    private @NotNull List<String> tabCompletePermission(@NotNull String typedNode) {
+        StringBuilder permissionListString = new StringBuilder();
+        if (typedNode.contains(",")) {
+            String[] permissionList = typedNode.split(",");
+            for (int i = 0; i < permissionList.length - 1; i++) {
+                permissionListString.append(permissionList[i]);
+                permissionListString.append(",");
+            }
+            typedNode = permissionList[permissionList.length - 1];
+        }
+        String permissionPrefix = permissionListString.toString();
+        List<String> output;
+        if (typedNode.contains(".")) {
+            List<String> matchingPermissions = permissions.get(typedNode.substring(0, typedNode.lastIndexOf(".")));
+            if (matchingPermissions == null) {
+                if (permissionPrefix.isEmpty()) {
+                    output = new ArrayList<>();
+                } else {
+                    List<String> onlyPrefix = new ArrayList<>();
+                    onlyPrefix.add(permissionPrefix);
+                    output = onlyPrefix;
+                }
+            } else {
+                //Filter by the typed text
+                output = filterMatching(matchingPermissions, typedNode);
+            }
+        } else {
+            output = plugins;
+        }
+
+        //Add previous permissions in the comma-separated lists as a prefix
+        if (permissionPrefix.isEmpty()) {
+            return output;
+        } else {
+            List<String> prefixed = new ArrayList<>(output.size());
+            for (String matchingCompletion : output) {
+                prefixed.add(permissionPrefix + matchingCompletion);
+            }
+            return prefixed;
+        }
+    }
+
+    /**
+     * Find completable strings which match the text typed by the command's sender
+     *
+     * @param values    <p>The values to filter</p>
+     * @param typedText <p>The text the player has started typing</p>
+     * @return <p>The given string values which start with the player's typed text</p>
+     */
+    private @NotNull List<String> filterMatching(@NotNull List<String> values, @NotNull String typedText) {
+        List<String> configValues = new ArrayList<>();
+        for (String value : values) {
+            if (value.toLowerCase().startsWith(typedText.toLowerCase())) {
+                configValues.add(value);
+            }
+        }
+        return configValues;
+    }
+
+    /**
+     * Loads all permissions available from bukkit plugins
+     */
+    private static void loadAvailablePermissions() {
+        plugins = new ArrayList<>();
+        permissions = new HashMap<>();
+
+        for (Permission permission : Bukkit.getPluginManager().getPermissions()) {
+            loadPermission(permission.getName());
+        }
+    }
+
+    /**
+     * Loads a given permission into the proper lists and maps
+     *
+     * @param permissionName <p>The permission to load</p>
+     */
+    private static void loadPermission(@NotNull String permissionName) {
+        String[] permissionParts = permissionName.split("\\.");
+        if (permissionParts.length == 1 && !plugins.contains(permissionParts[0])) {
+            plugins.add(permissionParts[0]);
+        } else if (permissionParts.length > 1) {
+            StringJoiner pathJoiner = new StringJoiner(".");
+            for (int j = 0; j < permissionParts.length - 1; j++) {
+                pathJoiner.add(permissionParts[j]);
+            }
+            String path = pathJoiner.toString();
+            List<String> permissionList = permissions.computeIfAbsent(path, k -> new ArrayList<>());
+            permissionList.add(permissionName);
+
+            loadPermission(path);
+        }
+    }
+
 }
diff --git a/src/main/java/net/knarcraft/blacksmith/container/ActionCost.java b/src/main/java/net/knarcraft/blacksmith/container/ActionCost.java
index d5131da..49bc2a7 100644
--- a/src/main/java/net/knarcraft/blacksmith/container/ActionCost.java
+++ b/src/main/java/net/knarcraft/blacksmith/container/ActionCost.java
@@ -28,6 +28,46 @@ import java.util.Set;
 public record ActionCost(double monetaryCost, int expCost, @Nullable ItemStack itemCost,
                          @NotNull Set<String> requiredPermissions) implements ConfigurationSerializable {
 
+    /**
+     * Changes the monetary cost of this action
+     *
+     * @param monetaryCost <p>The new monetary cost</p>
+     * @return <p>The resulting action cost</p>
+     */
+    public ActionCost changeMonetaryCost(double monetaryCost) {
+        return new ActionCost(monetaryCost, this.expCost, this.itemCost, this.requiredPermissions);
+    }
+
+    /**
+     * Changes the experience cost of this action
+     *
+     * @param expCost <p>The new experience cost</p>
+     * @return <p>The resulting action cost</p>
+     */
+    public ActionCost changeExpCost(int expCost) {
+        return new ActionCost(this.monetaryCost, expCost, this.itemCost, this.requiredPermissions);
+    }
+
+    /**
+     * Changes the item cost of this action
+     *
+     * @param itemCost <p>The new item cost</p>
+     * @return <p>The resulting action cost</p>
+     */
+    public ActionCost changeItemCost(@Nullable ItemStack itemCost) {
+        return new ActionCost(this.monetaryCost, this.expCost, itemCost, this.requiredPermissions);
+    }
+
+    /**
+     * Changes the permission cost of this action
+     *
+     * @param requiredPermissions <p>The new permission cost</p>
+     * @return <p>The resulting action cost</p>
+     */
+    public ActionCost changePermissionCost(@NotNull Set<String> requiredPermissions) {
+        return new ActionCost(this.monetaryCost, this.expCost, this.itemCost, requiredPermissions);
+    }
+
     @NotNull
     public String displayCost() {
         StringBuilder builder = new StringBuilder();
diff --git a/src/main/java/net/knarcraft/blacksmith/property/CostType.java b/src/main/java/net/knarcraft/blacksmith/property/CostType.java
new file mode 100644
index 0000000..017cc57
--- /dev/null
+++ b/src/main/java/net/knarcraft/blacksmith/property/CostType.java
@@ -0,0 +1,49 @@
+package net.knarcraft.blacksmith.property;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * The type of costs applicable to an advanced cost configuration
+ */
+public enum CostType {
+
+    /**
+     * A monetary cost from an economy plugin
+     */
+    ECONOMY,
+
+    /**
+     * A permission requirement, rather than a cost
+     */
+    PERMISSION,
+
+    /**
+     * In-game experience levels
+     */
+    EXP,
+
+    /**
+     * A specific item is consumed
+     */
+    ITEM,
+    ;
+
+    /**
+     * Parses a text string denoting a cost type
+     *
+     * @param input <p>The input to parse</p>
+     * @return <p>The parsed cost type, or null if not matched</p>
+     */
+    @Nullable
+    public static CostType parse(@NotNull String input) {
+        String normalized = input.trim().toUpperCase();
+        for (CostType costType : CostType.values()) {
+            if (normalized.equals(costType.name())) {
+                return costType;
+            }
+        }
+        return null;
+    }
+
+}