Rare cars can be incredibly expensive to buy. Rare homologation specials that allowed those cars to run can be even more expensive. Such was the case for a Mercedes-Benz CLK GTR Roadster that crossed the auction block at an RM Sotheby's sale in Las Vegas last week.

The final price paid including the buyer's fee was $10,235,000.

The car is one of just six examples built (it's car number three), and it's essentially a race car for the road that's had its roof chopped off. Like most rare cars, it's barely been driven. According to the listing, it has just 170 km (105 miles) on its odometer, despite being two decades old.

The CLK GTR was built around the turn of the century as part of a homologation deal required of Mercedes-Benz to compete in the GT1 class in top-level endurance racing. That class was actually discontinued in 1999, but Mercedes-Benz made promises to folks who raised their hands with fistfuls of cash to buy said homologation specials.

Mercedes-Benz CLK GTR Roadster - Photo credit: RM Sotheby's

Mercedes-Benz CLK GTR Roadster - Photo credit: RM Sotheby's

The plan was to build 25 coupe versions but only 20 were built, plus an extra roadster. However, HWA, the motorsports outfit founded by AMG co-founder Hans-Werner Aufrech following the sale of AMG to Mercedes in 1999, built five more roadster examples in the early 2000s using leftover chassis.

The full racing version of the CLK GTR competed in both the 1997 and 1998 FIA GT seasons. In 22 races, the Mercedes team earned 17 wins and walked away with both the drivers' and constructors' championships in both seasons.

The CLK GTR Roadster was more potent than both the race car and the coupe, as it featured the latest evolution of the V-12 fitted to all versions of the CLK GTR. The V-12 displaces 6.9 liters and delivers 622 hp in the roadster, up from the 592 hp of the coupe. The race car had even less power due to regulations such as air restrictor requirements and a smaller 6.0-liter displacement. Power is routed to the rear wheels via a 6-speed sequential transaxle.

This CLK GTR Roadster wasn't the most expensive Mercedes sold during the recent RM Sotheby's sale. That honor goes to a 2013 Mercedes Formula 1 race car driven by Lewis Hamilton to his first victory at Mercedes, which took place at the 2013 Hungarian Grand Prix. The price paid including the buyer's fee was a cool $18,815,000.