err, no, it's not. I saw a BPPC/060 go for £330 recently. Bvisions sell for around £70. So that's £400 before you even have a tower case (elbox sell those for £150), keyboard interface (another £30), A1200 motherboard, harddrive, etc. Plus, you always pay a slight premium on eBay for "Buy It Now" items, so £550 may seem expensive to you and I but in reality that's around the price you should expect to pay if you want those rare retro items from eBay.
Prices have sky rocketed for Amiga PPC h/w recently simply due to high demand and extremly low supply. That's the way free-markets work. No point whinging about it.