But if you are an experienced Unix sysadmin, and buy a $100 PC on eBay and install Linux or BSD, then you will really see cheap!
What can you get for $100? A 3.0 GHz processor, 320 gig HD, 4 gigs of memory. Plenty powerful to browse the internet and read email, particularly if you configure your system not to run a lot of worthless daemons in the background. Some people might not even bother with a GUI, but just run X.
I've already got a full trademarked version of UNIX™ on my Mac. It came with it. Why should I do something that requires me to spend most of my time working ON my computer rather than WITH my computer, accomplishing useful thing? I've been there and done that, through with that long ago!