It's not cheap either, but that's a given.
There are a lot of big, impressive car collections in the United States, and when it comes to rare and exotic cars, there haven't been many you couldn't get here at some point or another. But the king of unavailable exotics would probably have to be the Porsche 959, the fastest car in the world when it debuted, but one which Porsche decided not to bring over to the country which has been the biggest market for the Stuttgart brand for decades.
That's not to say that some don't make it over, one belonging to Bill Gates being the most famous example, but here is another of what must be a very small number. The car is for sale through Copley Motorcars near Boston. It has 10,000 miles on it, all of the necessary authenticity paperwork, and looks to be in excellent shape. Which naturally means the asking price is $1.4 million. This is a "Komfort" model, not quite as hard-edged as some of the others. It would probably be slightly less expensive in Europe, but these cars aren't cheap anywhere.