Luckily I have a guy locally who runs a tire/wheel shop so I get mine for killer prices. Check locally to you. Find the smaller shops with a low overhead, usually get a good deal that way. I prefer to support local shops over buying online.
When i purchased mine i had purchased mine at discount tire. 900 out the door siped, mounted, and balanced with a full coverage replacement plan if i were to pop a tire or something. I'm running 31x10.5.
Sometimes pays to check a local tire joint. I always like dealing with Tirerack.com but found a local shop that gave me a price slightly cheaper than tirerack once I factored in shipping, mounting, disposal, etc.
I work for a dealer here in beaverton and I have to say either tire rack or Americas tire seems to be the best place to purchase tires at a reasonable price. My last set of tires only cost me about 700 dollars, I did get A/T's and paid one of my tech buddies under the table for installation cost me about another 75 buck but totally worth it.