Good prices are extremely hard to come by on the market. Purchasing a city results in cash in your bank. Put your bank back on the market after building it up for a while. Although it will cost you coins, this is a good way to generate a lot of money.
Typically, purchasing real estate on the open market will cost you more money than it is worth. Generally speaking, I only invest in purchasing cities, towns, villages, marinas, and sports arenas. Instead of 50 or more coins when bought outside of the market, these items cost 1 coin to bid on. Both in terms of daily rent and resale value, they will often provide you with a superior return.