This cheat is most safely done when you begin the game.

At the start of the game you will have a bad car, then when you have done everything it tells you.

After that go to free ride and get the cops on you. Smash stuff so you get fined heaps of money, then you accept the fine and do it lots more.

Then go to the garage and look at your money, it will say minus so many dollors.

Then go into car showroom and choose the cheapest car there. Then go trade in and buy.

Then the rest of your money won't be minus and you can spend it on your car!