After you've completed the Malibu mission "The Job", you can rob El Banco Corrupto Grande for some easy money. Walk in and turn right up the stairs. This will earn you a four star wanted level. Walk into the manager's office to get 1/3 of the cash. The rest is in the room with the elevator, on the right side. Then jump off the balcony and run out. To shake the cops, you can turn left to the nearby Pay N' Spray. It's not much, but it's easy cash.