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.
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.