What's a '66 Barracuda Formula S, 4-speed project car worth?

Old mopars are generally worth more in parts than a project. Plenty of rust. You will always find more when you sand, take it apart. Mileage, who knows, Condition is everything. First gen cudas are not worth a million $ ever. You better be able to do the work or like said you will have $25000 in a $10000 car.
Buy it if you will love it and afford it all. That is why it is for sale now.