Probably just play the main storyline and upgrade the club. It starts slow, but pretty soon you'll be swimming in dollars.
Hmm, that sounds like a bug or something... Or, do you have empty slots in the club due to club upgrades? Each slot will incur an upkeep cost and if there are slots empty, the upkeep will start to stack up.
If not, could you send me your save file somehow and I'll try to figure out where the money is going?