Ebay seller UMO88 was selling lots of ten or twelve 640 X 480 LCD displays a while back. They were going for about $200 - $300. I was kind of shooting for about $10 each so I never bought one. I think they were 6" screens but they actually looked about the right size to fit in the SE/30. I"ve tried holding up some of the "9") LCD panels and they usually seem a little large to fit in the SE/30 case.
However, these were displays, not whole monitors. One would still need electronics to drive the LCD dispaly.
Ebay/business, industrial & test/electronic components is often a good place to search for this kind of stuff.