I tried looking for the super-basic ones you mentioned, too, but I said screw it and just ordered and received one purchased from this store:
http://stores.ebay.com/Y-PLUS?_trksid=p4340.l2563
It was called "Arcade RGB CGA to TV and Video Composite converter"
It was $25 with $12 shipping...so a bit more than what you mentioned, but I'm really happy with it. The only gotcha is if you're looking at the PCB, it has +12V silk-screened next to where the sleeve of the power jack is soldered, but that is actually the ground and the center of the jack was +12V.