I was in Costco (Derby) last week and they didn't have any in stock at all, luckily I got mine there a few weeks ago for £599 + Vat. Makro were selling them for the same price so they may be worth trying.
Just go & register & get yourself a card. If you don't, you could run into all sorts of snags if you need to return it etc (they'd only refund the account holder).