Reposted from my reply on mmorpg.com:

The subscription may be just $5711/year, plus ~$1,500 for WotLK, but he's incurring quite a bit more in hardware expenses and electricity, more if he's cooling his play area like a server room (and he should be with all that hardware). I'd be surprised if he wasn't playing on a business account on his ISP in order to handle the bandwidth limits imposed by many consumer accounts. Hell, with that much hardware, I'd be playing in a server room with a raised floor, cabling, cooling, UPS', etc...

~Ripper