Where are you looking? I would simply call a local Realtor, as for the SOLD comps for the area, preferrably subdivision you are looking in. They should know what a comparable house is (+/- 300 sq ft and etc). Good luck. If you want just a ballpark estimate that may be off by up to +/- 20% go onto Zillow.com. They say themselves in their disclaimer that it is not 100% accurate and that someone wanting a more accurate number should speak with a local Realtor. Good luck.