This one-off Shelby sold at Mecum’s Spring Classic Auction in Indianapolis over the weekend for $1.3 million, making it the most expensive Mustang ever sold. Not only is it a one-of-a-kind, but it is also the fastest Shelby Mustang from the 60s, powered by a 427 cubic inch V8 from a Ford GT40. Shelby had originally planned to build fifty of them, but the $8,000 asking price was too hefty.