Unless they have a new program I'm not aware of, Costco doesn't sell cars - their Auto Buyer program is just a negotiated '$-over-invoice' deal with the fleet sales group at select dealers. Sometimes these are great deals, and sometimes not so great.

I am going to test their pricing on a '07 Lexus RX400h this weekend - given the rather poor sales numbers for this model, I'm hoping the markup is very low, otherwise I will need to go to another dealer and waste the day doing hard negotiations.