So there's this website called Goozex, which lets you trade games for points. I doubt that most will actually start trading their games, but just for signing up you get 100 points. Now that is the minimum amount that a game can cost, but it's enough to get a decent, older ps2, or xbox game. I wouldn't recommend buying pc games, as well, they're used, so there's an obvious problem with online play.
Anyways, I'll give two links, the top one is my referral link (you sign up through me, when you make your first trade it gives me some bonus points) The second one is just a general link to the site if you choose not to do my referral.
It's real though, my buddy just had Battlefront show up at his door, and I just got a tracking number for Burnout 3: Takedown for the xbox.
Goozex - Trade video games for Sony Playstation 3, PS2, Microsoft Xbox 360, PC, Nintendo Wii, Gamecube, PSP, DS, GBA, Dreamcast, Mac - Your game trading community