Do the last race in the game in rock quarry. Do that because it is the easiest and you get paid 16k each time, plus if you have a fixer at 200 then you get like 17,175 each time.
Note: Entering the code too slowly will not make the cheat activate. Also remember to enter in this cheat at the title screen.
UP, UP, DOWN, LEFT, A, B, B, A.