Finally got back to Costco tonight.
Well, it was too good to be true.
Old mate remembered me from last week, remembers talking about Michelins... looked up the price, looked at the card I'd jotted the prices on, looked back at screen and tells me he would have been quoting on Bridgestones (even though we weren't taking about Bridgestones).
Oh well, c'est la vie.
20" Bridgestone Potenzas RE050A not Michelins @ $380 each for 3 and 4th one free.
20" Michelin PS4S $430 each (no 4th free deal).
On the plus side I finally joined Costco.
Sorry about the walk up the garden path...