Remember that KBB, NADA, Edmunds, etc. are only guides and are based on depreciation with the "tweaks" coming from the mileage, condition, and options. The true market value of a vehicle such as the Viper is based on supply and demand and you can use sites such as Autotrader, Ebay, etc. to determine what these vehicles are selling for. The trade-in value will be less but the ultimate determination will be based on what you are willing to accept. Trading in a car on a new one has one advantage in that you only pay sales tax on the difference between the trade-in value and the price of the new car. You will then need to assess the cost savings from the sales tax tax against what you would get by selling the car yourself if you have that option from a timimg perspective.