They made 1806 Boss 351 Mustangs. Only 500 or so have been accounted for. I have seen prices all over the board on these cars. I have seen prices range from 50K for cars that need some work to 90K for a rotisserie restored car. Just like any make of car originality and quality will dictate the price. Make sure the dual point distributor is there as well as the Autolite 4300D carburetor. This carb alone is worth 3-4 thousand dollars. Check out this web site for more information
www.boss351registry.com
Hope this helps
Mike