If you're looking for an authentic EGA monitor, or if 21 inches just isn't quite enough real estate for you, sorry.
That being said, and outfit in St. Louis, Business Systems Connection,
http://www.bizsyscon.com has a heap of KDS KVS-21 21" Pixeltouch Monitors for sale for $75.
Pros: They are kiosk monitors so they are designed to be mounted in a cabinet. These are not touch screen monitors. They work fine with a regular PC video card. The drivers can be pulled down from the web.
Cons: They're used - the one I have has some screen burn that I can just make out if the screen is set to the right color, and their power and adjustment buttons are in a weird locations (behind little holes in the left side of the case).
They've got a couple for sale on E-bay right now (in a lot of two) but if you call them you can buy just one.