If this is something that others have already tried and/or are using, pardon me for being redundant -- I'm always happy when I find something (in my budget) that seems to work well, and wanted to share. We don't own a guillotine yet, and are looking at something around $1000-1200 delivered for a Magra (a very nice tool from all appearances and reports). Kitchen knives have not cut it (so to speak) since it's hard to hold the beans and make the cut without risking digits. I remembered an old tool I've used in the past when installing a drip irrigation system -- a plastic tubing cutter -- and thought I'd give it a try.
A trip to the hardware store and $15 later, I am the proud owner of what appears to be a pretty serviceable one-bean-at-a-time solution. I cleanly cut 25 beans in just a couple of minutes -- way better than I've been able to do with a knife and cutting board. Here's a picture of the cut beans and the budget single-bean guillotine: