The only thing I've found so far is the WoW game itself is $19.99. Gamestop is selling BC, WotLK, and Cataclysm all for $79.99.
So everything WoW for $99.98. But you still have to buy the $15 monthly fee, so around $115 (plus taxes from Gamestop). I've spend a couple of hours looking around and this was the cheapest I found.
If anyone finds anything cheaper, please let us know!