I was hoping for $20 to $40.

Visit a few second-hand and thrift stores like Goodwill, Salvation Army, ReSale, and many others. Visit a shop in a wealthy neighborhood, they'll likely have a bunch of computer screens piled in a corner for that price range. It may take a few stores to find the ones where computer parts pile up, usually they're in the wealthy neighborhoods where people will dump functioning monitors in favor of newer, bigger, brighter monitors.

I'm thinking about second-hand screens as well. But it is a gamble! You will have no idea about its good or not in a short period of time.

You get what you pay for :D