MDD are getting cheap because mac OSX is x86 only these days. If you wait for the bottom to fall out you can get any mac for next to nothing, but at that point does anyone still want it?

I got the Quickisilvers because I like native OS 9.x booting macs, after the early MDD models I don't think they do that anymore. My B&W g3's were free or close to it when I got them, and my G4 sawtooth was pretty much just for shipping (got it to do a dual g4-500 upgrade but the board revision won't allow it).