Well........I am looking at two different buffers, but the one that is making the short list is this one:

http://www.harborfreight.com/6-inch-buffer-94393.html

It's $45. I know some people hate HF stuff, but I need something cheap to get me started and then I can move up to something more costly later.

This is also a thought, but at twice the price is probably not. Serious contender:
http://www.harborfreight.com/8-inch-buffer-40668.html

Or, we have an old washing machine that the transmission has gone out of that I could steal the electric motor from. That would probably work. Might be money ahead to buy the premade one though, by the time I bought everything else to make one though.