Simple Money Making:
In this guide I will be telling you how to make actual cash. Not where to get items or item drops, because currently there are no places to sell your items.
Kill Jadinkos at the Jadinko lair at ::Jadinko. These guys drop anywhere from 50k up to 500k. They will not drop cash every single time, but almost. You could make 1m in about 5 minutes.
Kill Polypore minions or the Ganodermic Beasts at the Polypore dungeon. These have less hitpoints than jadinkos, but don't drop nearly as much cash. So it is harder to distinguish this method as being better or worse than Jadinkos. My personal opinion is to kill Jadinkos, but do what ever method you feel gets you the most cash, the quickest.
As of now I have no other methods of getting just coins off the ground. There are other guides though on how to kill Bandos and other bosses which will give you drops of value, but not coins.