Win auctions: 
Start an auction. Immediately save the game when the auction screen appears. Quit the game and reload your saved game. Almost all of the time, the CPU players will pullout of the auction, allowing you to get the property for the cheapest price. If this does not happen, reload the game and try again.

Megapolitan bonus scenario: 
Finish all scenarios with any character. After the ending sequence, you be given a new scenario to build a Megapolitan. You will have $200,000,000 to build it, with no rival leaving you free to build your own city.

If you start a game any game in single player. build a apartment as high as you can to get some funds. Now. first and formost. start bidding on the 4 utility companies. After that. bid on all the railroads. Make sure you leased all 8. Within 2 - 3 days you will make between 4000 - 10000+ at 6 am. I do not know if this is a bug. but it will almost gaurentee you a winning game. after you play your money right.