I use Zillow to give me a ballpark number for prices in an area I don't know well. My experience is that they are usually within 20% of the market price, which

I use Zillow to give me a ballpark number for prices in an area I don't know well. My experience is that they are usually within 20% of the market price, which coincidentally they say on their website. For a free automated service, Zillow is great. If you want a better number, do your own comp analysis, or hire an appraiser.