When I looked it up on http://www.nadaguides.com I got around $4600 as the average retail but I didn't put in the AC. If it's really in good shape then the high retail might make it worth a bit more. Use the web site and select 'classic cars' and then collectible cars to get to the Mustang II. They're not a real popular car among most of the Mustang crowd but I feel they are a nice car. Because of the lack of popularity though,body and trim parts are difficult to come by.