Betson also has those new 27" Makvision Tri-sync CRT monitors. They're a little cheaper than Happ too.
If $500 is more than you want to spend, maybe say what your budget is.
Unless you get lucky on a used one, any decent monitor is going to cost around $500. Sony made a 20" 480p LCD but you never see them for less than $700.
There are a few Ikegami TM20-17r 20" CRTs on eBay but they are also $400-$500.
If money is that tight, there are still plenty of free or nearly free CRT tv's on Craigslist. Just get a newer Sony model with component video.