You essentially have a few options:
1. Find the same model home in the area that is for sale and update it to look like the home you are interested in.
2. Search online to see if the home is in pre-foreclosure, and then anticipate trying to buy if it gets foreclosed.
3. Search public records and estimate what the loan balance is on the house. If the house was purchased between 2002-2009, it might be underwater and you could potentially contact the homeowner to see if he is willing to participate in a short sale.