Eh, if your town has a recycling center, go there. Most small towns and many large ones will just hand you old computers for the sake of them not having to pay to dispose of them. I know in my (tiny) town, peope cannot throw computers away. We have to bring them to the town highway dropoff. There's a trailer there with 20-40 old computers on any given weekend. The guy running the place will let you walk in and take them if you don't try to piece them out right there (you have to take the whole thing).
It's like an endless supply of low end machines for free. Monitors are dead as often as not, though, and not worth the $7.50 to bring them back if they are.