A friend of mine has his computer hooked up to conventional speakers that are wired outside his house. He uses a guitar amp and tells me I can use a simple stereo receiver to achieve the same results.

My question is, does anyone know where I can by a simple amp to connect to my computer without spending $100 or more for the stereo or the expensive amps?

I dunno exactly where you should look for an amp, but I know you'll most probably need some kind of minijack to tulip plugs cable, which you should be able to find at your local radioshack
I have the same setup, 2 bigass regular speakers with an old amp that was destined for the garbage dump. I reckon this has to have the best price/quality ratio