Cheap purchases
Play against the CPU and land on an unowned property. Place the property up for auction. Keep bidding $10 to win the auction as no other player can challenge your offer.
Cheat mode
Enable the "Cheating is allowed" selection under the "Custom rules" option by clicking on it. Then, press [Plus] when rolling the dice to move one space forward or [Minus] to move one space back.
Unlimited money
Type I'm Bill Gates, I'm VERY rich! (case-sensitive).
Cheat mode (WM edition)
Type gimmesheep during game play.