Good condition and historical significance make for a hefty price tag.
The original line of Shelby Mustangs really didn't last all that long. Carroll Shelby's speed-obsessed minimalist approach clashed with Ford's apparent need to add as much bloat to as many of its models as possible from the end of the sixties and going into the Seventies. This all culminated in Shelby pulling his name from the project after the 1969 Mustang redesign rendered so much of his work irrelevant. But Ford still wanted to sell the cars.
So some loopholes were found, and Ford was still able to offer a handful of 1970 GT350 models, including the one you see here. In fact, this GT350 was the last one to roll off the assembly line, and has the dubious honor of being the only GT350 fastback to have been built with an automatic transmission. The car has had two owners, and spent all of its time since it left the factory in Florida, thus never seeing a winter. It was lightly restored in 2006, but was never used much, and only needed touching up. It is now being auctioned, and it is expected to go for between $200,000 and $250,000.