Depends what you're after and how much you're offering.
I just picked up an F100, firmware 4.0, with modded joystick... bare console, no AC or case, etc., but with a 512Mb SD card (actually an SD-Mini inside an adaptor) from eBay. It was so new and shiny, even the power switch was extremely stiff - I don't know who had it before, but they can't have played on it much at all.
I think it cost me about £45-50, all told. What were you looking at offering and what parts did you want with it? (TV-Out, AC Adaptor, etc.)