I just bought one $20.. used 17" envision En-710e almost new (9 month old)..check local lists and stuff like that .. I am closed to Boston and when students pack their items they usually leave big monitors behind..
so check lists of local schools..
I used
www.craigslist.org to spot my monitor.. you may even see free 21" nec monitor (damn I missed that one though a bit old)