Keep in mind, while you dont have to pay sales tax and disposal fees, you do pay shipping and still have to get the tires mounted/balanced locally unless you do it yourself.

This can often times equal out in price and if you buy locally then if you have any problems with the tires or need to get them rebalanced, etc they will do it for free (ie: Discount)
Most people dont know, but tire stores will deal on tires. Shop around, dont settle on the price they state. Its like buying a rifle or a car - they will always negotiate price.