Well, if you don't want to pay Gamestop's prices, check Game Crazy. Silent Hill 2 is $9.99 used(pretty sure it's still that price) and Silent Hill 3 & 4 are $12.99 used each. Prices are the exact same for the PS2 & Xbox versions of 2 & 4.
This seller has all three of these for PS2. I have traded with her before and she is very reliable. Make her an offer and she will most likely give you a great deal.