I can't see why anyone would buy a G4 these days for their main machine , its just too old and not supported by new apps/OS/parts anymore.

$39 for a dual MDD is a good deal for a collector who can fix things, but most people would pass on a stripped non booting one. G4 towers got so cheap that I could not resist getting 2 of them (Quicksilvers). G5's still seem pricey to me (last of the PPC line I guess).