Need for Speed Carbon

The cheat codes don't provide a lot of money. If you're on a PC, you could use a trainer to set lots of money. Since the game has a "my cars" garage, that doesn't involve using career money, normally this isn't an issue unless you want the reward for 1 million cash in your career. To do this, you need to not spend much on the cars during career. It's actually possible to not spend any money at all, because the game handicaps, so you can just use the car you start with, not upgraded, then use the boss cars as you win them. This strategy requires you turn off autosave so you can re-run boss races if you don't get the pink slip via a random marker, and only save after a good run.

Kenji's RX7 is fast enough to win career mode with, if you use a lot of speedbreaker. The cheat codes for infinite nitrous and infinite speedbreaker work in career mode, making this a bit easier. Speedbreaker doesn't apply during the canyon races, but the RX7 combined with the games handicapping is enough to win.

You don't have to go to this extreme, but note that getting all rewards involved selling all of your career cars in order to get a full garage of exotics, muscles, and tuners for those 3 rewards, so only do minimal upgrades to the cars, since you won't be keeping them if you want to get all rewards. Usually street tires and nitrous is enough, again, because if you're slower, so are the computer opponents.