Where is the cheapest place to buy Pokemon Games?

I would like to collect all the Pokemon games, but most places are really expensive. I've tried Ebay, but they are still $20 each, even for the older ones! I understand paying that for the newer ones, but at $20 for Gold is just a scam, and I dont have that much money. So is there anyplace where I can get some of the 1st and 2nd gen games for like $5??