Phone 3 dealers and ask them for a trade in value.
Scan Autotrader for similar year models and it should give you retail value. Be prepared to expect a huge difference.
Phone your insurance and ask them what the value of the vehicle is (and how they value it - e.g. retail value, replacement value, etc). If it is your current vehicle, should be easy. If it is a vehicle you don't have, tell them you're thinking of purchasing and after all the questions, they should give you the insured value.
May not answer your question directly, but hope it helps ...