Lowest I ever saw sold for 3m, in the swamp. Otherwise they are closer to the 5m range and up like Holden said.
For reference purposes only: Swamp - 3-5 mil usually Ice - 4-6 mil usually Jungle - 5 mil and up Grass - 6 mil and up Bonus features such as mining, waterfront, seclusion, etc add mils to all the above listed prices. Nothing's etched in stone when it comes to house prices, but this should help you get a feel for what to expect.