DropCommand

package main.java.net.bigbadcraft.dropmoney;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

public class DropCommand implements CommandExecutor {
	
	private final ChatColor GREEN = ChatColor.GREEN;
	private final ChatColor RED = ChatColor.RED;

	@Override
	public boolean onCommand(CommandSender s, Command c, String l, String[] a) {
		if (s instanceof Player) {
			Player player = (Player) s;
			if (c.getName().equalsIgnoreCase("dropmoney")) {
				return command(player, a);
			}
		}
		return true;
	}
	
	private boolean command(Player player, String[] a) {
		if (a.length == 0) {
			player.sendMessage(RED + "Incorrect syntax, usage: /dropmoney <amount>");
			return true;
		} else if (a.length == 1) {
			try {
				int amount = Integer.parseInt(a[0]);
				player.getWorld().dropItem(player.getLocation(), getPaper(amount));
				player.sendMessage(GREEN + "Dropped: $" + amount);
			} catch (NumberFormatException e) {
				player.sendMessage(RED + "Please enter a number for your second argument.");
			}
		}
		return true;
	}
	
	private ItemStack getPaper(int amount) {
		ItemStack paper = new ItemStack(Material.PAPER, 1);
		ItemMeta meta = paper.getItemMeta();
		meta.setDisplayName("$" + amount);
		paper.setItemMeta(meta);
		return paper;
	}
	
}

InventoryClickListener

package main.java.net.bigbadcraft.dropmoney;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.event.inventory.InventoryType;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

public class InventoryClickListener implements Listener {

	MoneyPlugin plugin;
	public InventoryClickListener(MoneyPlugin plugin) {
		this.plugin = plugin;
	}
	
	@EventHandler
	public void onClick(InventoryClickEvent event) {
		final Player player = (Player) event.getWhoClicked();
		if (event.getView().getType() == InventoryType.ANVIL) {
			if (event.getRawSlot() == 2) {
				if (event.getView().getItem(0).getType() == Material.PAPER && isMoney(event.getView().getItem(2))) {
					event.setCancelled(true);
					player.sendMessage(ChatColor.RED + "Do not even attempt to exploit DropMoney.");
				}
			}
		}
	}
	
	private boolean isMoney(ItemStack i) {
		if (i != null) {
			ItemMeta meta = i.getItemMeta();
			if (meta != null) {
				String name = meta.getDisplayName();
				return name != null && name.startsWith("$");
			}
		}
		return false;
	}
}

MoneyPlugin

package main.java.net.bigbadcraft.dropmoney;

import java.util.logging.Level;

import net.milkbowl.vault.economy.Economy;

import org.bukkit.Bukkit;
import org.bukkit.plugin.RegisteredServiceProvider;
import org.bukkit.plugin.java.JavaPlugin;

public class MoneyPlugin extends JavaPlugin {
	
	public static Economy economy = null;
	
	@Override
	public void onEnable() {
		if (!setupEconomy()) {
			Bukkit.getLogger().log(Level.SEVERE, "Vault not found, disabling DropMoney");
			getServer().getPluginManager().disablePlugin(this);
		} else {
			setupEconomy();
		}
		getCommand("dropmoney").setExecutor(new DropCommand());
		getServer().getPluginManager().registerEvents(new PlayerInteractListener(this), this);
		getServer().getPluginManager().registerEvents(new InventoryClickListener(this), this);
	}
	
	private boolean setupEconomy() {
        RegisteredServiceProvider<Economy> economyProvider = getServer().getServicesManager().getRegistration(net.milkbowl.vault.economy.Economy.class);
        if (economyProvider != null) {
            economy = economyProvider.getProvider();
        }
        return (economy != null);
    }
}

PlayerInteractListener

package main.java.net.bigbadcraft.dropmoney;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.Action;
import org.bukkit.event.player.PlayerInteractEvent;

public class PlayerInteractListener implements Listener {
	
	MoneyPlugin plugin;
	public PlayerInteractListener(MoneyPlugin plugin) {
		this.plugin = plugin;
	}
	
	@EventHandler
	public void onInteract(PlayerInteractEvent event) {
		final Player player = event.getPlayer();
		if (event.getAction() == Action.RIGHT_CLICK_AIR || event.getAction() == Action.RIGHT_CLICK_BLOCK) {
			if (player.getItemInHand().getType() == Material.PAPER) {
				String display_name = player.getItemInHand().getItemMeta().getDisplayName();
				if (display_name != null && display_name.startsWith("$")) {
					int cost_amount = Integer.parseInt(display_name.substring(1, display_name.length()));
					int player_balance = (int) Math.round(MoneyPlugin.economy.getBalance(player.getName()));
					MoneyPlugin.economy.depositPlayer(player.getName(), cost_amount);
					player.sendMessage(ChatColor.GREEN + "Deposited: $" + cost_amount + " into your account. (Total: $" + player_balance + ")");
					if (player.getItemInHand().getAmount() > 1) {
						player.getItemInHand().setAmount(player.getItemInHand().getAmount() - 1);
					} else {
						player.setItemInHand(null);
					}
				}
			}
		}
	}
}