A particularly valuable example of an already valuable car.
It would be difficult to say exactly which of the classic muscle cars is today the most valuable, but Ford's Boss 429 Mustang is likely to be it, thanks largely to its rarity. The Boss 429 was built only for NASCAR homologation purposes, as a way to compete with Chrysler's legendary 426 HEMI, and a mere 859 units were therefore created. These cars actually started as 428 Cobra Super Jet Mach 1 units, and were extensively modified by Kar Kraft to make the new engines fit.
Officially listed horsepower was rated at 375, but actual output was at least 500, and some say 600. The small production run was for the 1969 and 1970 model years only, and now one of the 1969 models is being sold by a Dutch dealership out of Willemstad, known as Classic Master. The asking price is €350,000 ($456,190) which would be one of the highest prices ever fetched for a Boss 429. But the mileage is listed as 1, and these cars are obviously even more rare in Europe, so this isn't altogether surprising.