Realtytrac is a service that tracks foreclosures. It is a subscription only service and many times the houses are not actually up for sale at all. The owner just hasn't paid the mortgage. Realtytrac tells you exactly which stage the foreclosure process is at: Lis Pendens, bank owned etc. The value amount that you see on these homes is the amount required to pay off the loan. As the house may not even be on the market, this amount doesn't always correlate with what the owners would accept or even whether the house is worth more. For example, an $800,000 home may have a $400,000 mortgage and the owner has fallen behind in his payments. Realtytrac will show the value for the house at $400,000 because they are just showing the mortgage amount.
Hope this helps!