I would try the Goodwill near you.
I picked up an excellent condition Sylvania 19" for $20 a couple months ago.
They had 3 or 4 other ones at the time, as well.
Alot of people are upgrading to 17" flat-panels, and can't get rid of their 19" CRTs, so they go off to the Goodwill.
Garage sales, ebay, and classifieds are other good sources.
Just make sure you set the search radius in ebay's "advanced search" to however far you're willing to drive.