If you're playing against a single computer opponent then this trick will save you some serious cash. When entering an auction, simply bid $1 above your opponent. He'll give up on the second round.
The easier way to win in this game is to buy one of each property, starting from the purple to the orange. This way the computer can't build houses.
Start with $4,500
Start the game as usual but select three players on controller 1. On your turn, make deals with each of your fake players for their money. When it's your other players' turns (the ones with no money) go to "Bankrupt" and then play the computer as usual. You now have $4,500.