I usually check the tire(with the size) that I want to buy from http://www.tirerack.com/index.jsp(they have the ranking for the tires that you need.). Then call those garages for the price of tires you'd like.
Wal-mart,Canadian Tires and Costco usually have a better price. But check by phone for all those garages that can do a tires job. I found the best price for my SUV in last summer from a garages in Carling ave. close to Volvo dealer.