I would ask the out of state dealer about how the taxes work, I'm pretty sure I'm paying my instate tax rate, not the out of state taxes even though the dealer is there. Still I don't know how great a Costco dealer would be since the experience is supposed to be "no haggle" - so pretty inflexible.Good to know. So far my quote with X-plan and minor incentive is just under MSRP before fees. Probably will end up close to sticker but he assured me they can wiggle some stuff and make up the contract before delivery to find the best options.
I found a Costco dealer which was a long way off, and after presenting payment estimates from the x plan, he hung up and hasn't called back. I'm guessing his guarantee that costco was better than X-plan was off by a few bucks. Found another Costco dealer much closer but over the state line, their taxes are higher so I didn't even bother following up.