I designed my study plan (in the sidebar) around cheap computers. At the time I wrote it, I thought good Linux-ready desktops were going for around $50. That wasn't much to spend if you couldn't find one in your closet.
I'm browsing Craigslist right now, and I'm kind of amazed. There are some good notebooks for less than $100. As an example:
IBM Thinkpad T43, Wi-Fi, 1.86Ghz, 1GB, Fantastic Condition - $80
I think we might be about to ubiquitous computing. From this point on computing power is approximately free. Of course, you can still drop a thousand on a new Mac notebook ... for however long that lasts.