Even if you've never built a PC before, if you feel brave enough to give it a try I would highly reccomend that route. For under $1000 you should be able to purchase all of the components you'd need for a rig with more than enough power to handle 5 accounts in Dalaran.

If you just don't want to go near trying to assemble yourself, Owltoid's reccomendation is great and a far better price than Alienware, or other "name" systems.