What is the rarest car in US?

The rarest automobile built in the USA for the domestic market is the 1967 Shelby G.T. 500 Convertible. Though many were planned as a mid-year offering, only a single example was built at the start of that year's production. Only a single car was built and it survives to this day in private hands. The car was not a prototype nor experimental. It was built on Ford's San Jose, CA assembly line, meeting all Federal safety standards with the intention, and end result of being sold to the public for use on public roads.

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There is no "rarest car", but some concepts and things worth the most are the Chrysler diablo, and the Maybach Exelero