I trying find a good mod which add a coins (and economy) but any is not good enough for me.
So i made one.
Mod adding a few things:

1) Coin of value: 1,5,10.20,50,100,500,1000
You can spare coin in crafting bench.
For example: 2 coins 50 equal 1 coin of vaule 100
1 coin of value 20 gives you 2 coins of value 10 in crafting bench

2) Wallet,

If you rightclick wallet, you will open GUI.
Put coin above "+" button and press button, so you will donate account.
If you click button with negative numbers, you can withdraw coins.

/gamerule allowCraftWallet (default) true.

If you don't want be able to craft wallets, set this to false.
After crafting, wallet will be taken from player and materials gived back.
Wallet don't drop from anything. You can only craft him or get from creative.

3) Coin drop from mobs!
Coin 1,5,10,20.50,100 can drop from mobs.

But, which? You can set this using gamerules below:

/gamerule AllowDropCoinFromAnimals (default) false
Set drop for animal type.

/gamerule AllowDropCoinFromCubes (default) true
Set drop for slime, magma cube, shulker box.

/gamerule AllowDropCoinFromFlyingEntity (default) true
Set drop for flying entity. Vanilla: (Ghast, Phantom)

/gamerule AllowDropCoinFromGolems (default) false
Set drop for golem entity which Vanilla Golems is Snow Golem and Iron Golem

/gamerule AllowDropCoinFromMonsters (default) true
Set drop for monster type.

/gamerule AllowDropCoinFromVillagers (default) false
Set drop for Villager and Wanderer Villager.

/gamerule AllowDropCoinFromWaterAnimals (default) false
Set drop for water type example:fish

You can use this mod whatever you want.

1.2.1:
/eco <player> help 0 for admin (ops) use

CloudCoins