First, you'll need 2+ PS3 remotes to do this. Start up a Multi-player Story mode game. Log into Player 1 with your PS3's account name. Have additional players log into the game as a Guest. Now as player 1 pick the character who you want to give the money to and have the "guest" players log into the character with the most money on hand. Get to a shop and have the "guest" players lend all of their money over to player 1. Exit the map to save data, then Exit the Game. Repeat. Game only saves data for your character and not the guest characters playing, so all the money that was on the character for player 1 is saved when transferred while the money in "guest" players where not decreased.