Double prize money: You can double your prize money by racing an opponent
and having less than half of the green that your opponent is betting. Save
the game before doing so -- if you lose, you will also lose your car. If
you concentrate on the expensive mods first (after buying at least level 1
mod of everything), the other ones will be easy to pay off once you hit
class B/A, getting over $1,000 per race with this trick.