Last weekend was a big one for Mecum Auto Auctions. Their annual Indianapolis auction always draws a big crowd and some truly collectible cars, but this was one for the record books. Much of the attention was focused on the Gone in 60 Seconds Eleanor Mustang from the 2000 film, and that car sold for a cool $1.1 million.

Eleanor should have been the chart topper of the weekend, but there was another, even more valuable Mustang ready to roll across the auction block. That was a unique, one-off 1967 Shelby Super Snake, and when the gavel fell it sold for a jaw-dropping $1.3 million, the highest-selling Mustang ever.

What makes this particular Shelby so valuable? Basically, it is the only one of its kind, a prototype built to the highest specifications and performance aspirations. Originally prepared to showcase Firestone’s new Thunderbolt budget passenger cars, Shelby eventually stuffed a 427 V8 engine from the Le Mans winning Ford GT40 under the hood.

While plans originally called for 50 examples to be built and sold, the original GT500 Super Snake was too expensive to market to customers. Despite a 142 mph top speed, the $8,000 price tag was more than double what a standard Mustang sold for, and only one example was ever built.

With Shelby classics demanding an ever-increasing premium, it really isn’t surprising that this Mustang sold for a record price. That record will likely be broken when some other super-rare Mustang comes along. For now it stands as a testament to the collectability of these cars.

It’s an interesting comparison between today’s automotive market and that of the 1960’s. Today a GT500, not even a Super Snake package, costs double or more than a standard Mustang V6, the market truly has changed in terms of the premiums a customer will pay for a powerful performance Mustang.