Check to see what the banks in your area use to value the car. Some areas use Kelly, others use NADA. There will be slight differences between the two "book" prices. Kelly is usually higher, hence sell by Kelley, buy with NADA.
In addition to the websites previously mentioned, it never hurts to see if you can find similar vehicles for sale. Try sites like ebaymotors.com, autotrader.com, etc.
When you call the bank, get the trade in value. And then the retail. Besure and get the value by equipment on the car. Trade in value is usually the auction price at many large auctions.. or smoe wher close. also the loan value. good luck