22. 1931 Bugatti Royale Kellner
Ettore Bugatti only made 6 Royale models with enormous 13.9-liter engines. Each sold at an astronomical price when the car was released in the early ’30s. Despite the name, no king ever owned one and all six proved to be a tough sell due to its price.
Today, the Kellner version (Kellner was a coach-builder) is one of the most iconic Bugattis because of its rarity. It was sold for almost $10 million in the early ’90s. If an example went on sale today, it would most likely fetch at least double that figure as a result of its status as one of the rarest, most expensive classic cars on the market (via CarBuzz).