I'd be extra cautious about those $1700 4500s on EBay. I was in Boise over the weekend and talked to Kevin Hoagland of Minelab. He says it's really hard to find a 4500 right now. Seems there's a gold rush in Sudan. As a consequence, Minelab is trying desperately to fill 10,000 4500s that have been backordered. Minelab can't produce them right now because there's a component, which is not manufactured by Minelab, that is in very short supply. Seems the component is also used in making LCD TVs. Anyway, what it all boils down to is that if those EBay items really are working 4500s, they would probably command a much higher price.