The best and most common way for Realtors and banks to arrive at an asking price for a short sale or bank-owned home is to look at comparable sales, pendings, and listings, get an average value then adjust for the subject property's condition and location.
What you should offer for the home will depend on three factors- the buyer's motivation, the seller's motivation and the amount of competition from other buyers. Every situation is different, so you will need to consult with a specialist in order to determine the best strategy for you and the home(s) you are considering. I'd be happy to help you, if you'd like.
Real Estate Consultant
Certified Foreclosure Specialist
Certified Short Sale Specialist
Bank-Owned Property Specialist