MacMini G4 : 250/400 E (depending cpu speed, HDD, CD or DVD or DvdRW drive...)
Mos 2.4 : 150E ...
Like Atari Jaguar's add said " do your maths...!!"
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.