People can sell their Amigas for whatever they want to ask for them! You don't have to buy it, so get over it.
That being said, I look at every single one of these auctions and I would definitely pay this kind of money for an Amiga 1000 with the original Boing Ball logo - which was the badge the Amiga 1000 was being sold with before Commodore purchase the rights to the Amiga.