(Really) Fast glass + limited supply (+ cult status) + optimized for night/low-light/wide open shooting = high prices

It's a specialty lens, that, as others have said is outstanding wide open (where most others are at their weakest), but stopped down, is very average. For general purpose shooting, you're likely better served with a more conventional lens, but if you need sharpness wide open at night, there's few better, and for that distinction, you're going to pay for it.