Similar, in many ways, to a Ferrari FXX, only rarer.
GT1 homologation cars are always very rare, what with the FIA rules only requiring 25 roadgoing versions to be built in order to compete. But even rarer are the track-only versions of these cars. So as rare as the 50 units of the Maserati 12C are, they're downright plentiful compared to the 12 units of the 12C Corsa that Maserati built for some very rich and very well connected track day enthusiasts back in 2006, toward the end of the 12C's production.
The cars share quite a bit with the Ferrari FXX, since they're both tracks versions of the same chassis and use the same engine. One of them, #2, has just popped up for sale in Fort Lauderdale, Florida. It's still wearing the original “Blue Victory” paint, and apparently has only 89 km on it. The asking price is $2.99 million, which is about double what it cost new. Not a lot of cars have been known to double in value over the course of just a decade, but then again, we're dealing with something so rare that normal market forces don't really apply. We'd be curious to see if the seller gets that price.