That's exactly what I was thinking about when I noticed the VGA input on the monitor, but those converter boxes normally run you $50+ which I just can't justify spending considering the RasPi didn't even cost that. The main reason I've been trying to find something to work with the RCA input anyway is because I'm using the Pi for interactive fiction development (which does not require a high res display by any means). I had the Pi plugged in to my old big screen and it (mostly) worked but the picture would always be slightly larger than the screen, which caused problems any time I ran certain programs.
I figure I'll plug it in and see what happens. If it works, great! If not, it was only $3 and I can still use the monitor to upgrade the horrible manilla behemoth my Ubuntu desktop is hooked up to (LOL).
I saw a few 15-20 inch HDTVs on sale for around $75-$80 that I might be tempted to pick up. At least they can also be used as a stand alone television in addition to the Pi's monitor.