They are the safety feature which hopefully prevents the use of all other safety features! They are as important as crash structures, HANS, even helmets.
They have to be removed in a huge hurry with high impact forces and have to go back on pretty quick with no slip-ups. It's absolutely right that they should be made from the best materials available and very tightly toleranced.
There has been plenty of slagging off of the price of the humble wheelnut on here lately, from many quarters, probably because they are seen as humble, in no way as exotic as a piston or even a brake calliper. Maybe they should be the first candidate for a one-make tendering process, but lets not look to save money here for the sake of it.
I handled one a while back, I think they are/were forged Titanium, a beautiful piece of kit and the price estimates I have seen on here and heard elsewhere range from £500/£2000 per piece, does anyone have any more info?