I own a Cobra Jet Mustang. How much is it worth?

There is no perfect answer to this question. Value is very much a matter of condition, original equipment, race history, and where you live. A rust-free car will always be worth more than a rusty car if all else is equal, and a car missing original equipment will always be worth less than a car that's complete. If you want to get a feel for worth you might try looking at the classified ads in Hemmings Motor News, or check out national auction results in the magazines that publish such info.