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Gamecube - R: Racing Evolution cheats

Get new cars without buy:
Go back into races where you can select cars.
Select a car you don't have and win with it. 

Getting money easily:
Play a drag race in event challenge mode. Beat Nelly.
You will get the Mazda RX-7. Repeat the race.
If you win again, you will get more than 100000RP.
Repeat the race as many times you want.