After you do the last mission go to the police station near the malibu(south of it) and get the cop uniform then jump in a cop car and go to the airport then to the army base and look in the back for The Hunter(A kickass helicopter with machine guns and missiles).

If you need money for anything you can get unlimited money by doing the following trick.

Get a cop car, go to a garage where you can store it, drive into the garage, start vigilante mission, get out and go outside of the garage for it to close, punch in R2 L2 R1 L1 L2 R2 square triangle circle triangle L2 L1(blow up all cars) and get back in it and repeat(at mission 50 or so you get 100K each time).