Explanation
Never Enough Currency is a mod which has currency loosely based on USD. The mod contains such things as an account system, ATMs, wallets, and soon™ an immersive shop system.
How Do I Get Currency?
Hostile mobs drop money based on the amount of health they have divided by the number 8. A immersive shop system will also be added in the next update for selling your items to other players.
The next update will also contain config options to give money each real-time day or in-game day with a configurable amount.
Mod Support
Any mod which has their hostile mobs implement IMob should drop money (most mods should work).