How much would you seriously expect to pay for one of the best PC games of the last few years? Sure, it came out in 2006, so it's getting on a bit. But still, it was easily worth $100 at launch.
Now though, thanks to a Steam special, you can get S.T.A.L.K.E.R. Shadow of Chernobyl for a piddling $US3.75. That is, in our local moneypoint, about four bucks.
I'm going to buy it again.