I noticed the same thing when I was helping my sister find some 31 for her Runner. I figured since she didn't wheel her Runner much she could go with the Procomp AT's and take advantage of the buy 3 get 1 free. Called the local 4wheelparts, and got a quote of over $700. I then called America's tire and got a quote on BFG AT's and it came in around $650. The buy 3 get 1 free is just another way to get impulse buyers to shop, since you don't get anything for free.

Your best bet is to shop locally, this way you don't have to wait to get a tire replaced if you get tread seperation, sidewall puncture, a balancingf problem, or pay to fix a flat. You can also play the local shops against each other, to get a better price on tires or getting the road hazzard upgrade for free, i.e., free replacement v. pro-rated.