This is a very easy method to get unlimited money on Dead Island, however, it is very time consuming.

1) Go to the warehouse.
2) Pick up the hammer and the baseball bat on the floor.
3) Fast travel to the church.
4) Sell both items.
5) Fast travel back to the warehouse.
6) The hammer and the baseball bat will of both re-spawned.
7) Repeat the process until desired money is achieved.

You should earn about $400 per run. This can be very useful for players just starting out.