I wouldn't sell it either, but did some digging to get you some numbers. The reason is because its hard to get a good price on anything now due to the downturn. Everyone is cutting back especially on discretionary expenses like sports cars.
The source below suggests a rust free car is worth at least triple the asking price or about $12,000. It seems to me this is a serious lowball estimate. You could hire an appraisal service, but I would just save the cash.
Bramhall Classic Autos - Appraisals
This Australian website has some valuation numbers in a table format. You dont say if its a V8 coupe, Fastback or a V8 Convertible but the numbers are between 28,500 to 42,000 for pristine condition cars. I think the numbers on this site are in Auzzie Dollars which need to be converted back to US Dollars at 0.65.
Ford Valuation and Pricing Guide
The other approach is to go to eBay and look at what similar cars to yours are selling for.