Enter multi-player mode and select the Peer To Peer option, but choose to race alone. You will be able to select any car on any track.

Purchase a used car and choose to do an Overall repair. When completed, the value of your car will be higher than the purchase price and the cost of the repairs. Sell that car, purchase another used car and repeat as needed.

Enter the following "names" in the create player
option for the cheat:
All Cars +933 Physical = "yraGyraG"
Enable Destruction Derby Mode = "smash up"
Make Cars Heavier = "fetherw8"
Cops in some Quick Races = "fuzzyfuz"
Enable RC Cars = "Gullivers"