Been looking at the MM's on EBay myself... But what exactly is MorphOS? I've read the website and I can't tell for sure. Is it a variant of the Amiga OS in some way?
Lets just say MOS is what AmigaOS would have been had C= not died and kept on with development. It looks, feels and acts like a modern day implementation of the Amiga, with loads of compatibility with modern REAL Amiga software, applications and games.
No idea who's ripping you off for a G4 MacMini, but you can buy a new Intel one for that money.
MacMini G4s are generally $200-$250 USD around here, and dropping due to lack of support in Snow Leopard.
I have to agree, keep off Ebay if you have access to craigslist. I neve use ebay now and I see G4 mini's going for $200-$300 all the time here in San Diego. I would get one if I didnt have a 1.25Ghz version, and it works perfectly fine for MOS, even with half the video memory the 1.5's have.