I am considering a 3.6R Outback and have considered switching out the OEM tires for a set of Michelins Primacy. I have these on my current vehicle and they are great.
What is the best way to do this? If so, I would like to buy the tires at Costco due to their excellent warranty and service.
I have the Primacy MXV4 on my Accord. They are great tires. I pretty much buy exclusively Michelin. That being said, I find the stock Bridgestone tires on the Outback (over 9000 miles) to be very good in anything but snow/ice conditions. I will be buying some Michelin x-ice tires next winter. You might find the stock tires acceptable. If not you can replace the stock tires and probably get some money for them on Craigslist, although I'm not sure how popular the 225 60R18 size is.
If you are still in buying process, after you've negotiated your price (so the dealer doesn't try to bundle it) ask the dealer to give you a credit for the new tires and to install tires you want (you provide the new tires). Dealers charge top dollar when customers need a new tire so it would be a money maker for them to have four new tires in stock to sell.
Saves you the work of selling on Craigslist which would be Plan B. Considering the MPG issues, you might want to look at Michelin's high MPG, low rolling resistance tires if MPG is important to you. Since you are getting the Xices (I have them for my Legacy put on as soon as I purchased the car in Feb) for winter, you can get high MPG tires for rest of the year. I got excellent MPG on the Xices.