Last Fall I bought a set of four 235/65R17 Bridgestone Blizzak DM-Z3 snow tires from U.S. online retailer Tire Rack for $656 all shipping, taxes, duties, fees and foreign exchange paid.
Cheapest Canadian price was from online retailer Tire Trends at $953 including shipping, etc. That's a $298 difference, 45-percent more.
Best local tire store price was $1,341 including McGuinty tire tax, PST and GST. That's a $685 difference, 105-percent more.
In all cases installation, balancing, etc. were extra.
Seems in the Canadian tire biz cutthroat competition drives prices up!