Best you could do is a 2U rackmountable (if AMD).. I'm suprised you would go tower.. unless some place charges you the same 1U or tower.. it's just not a good idea..
As for the price maybe I'm wrong.. but I think $1500 might be more reasonable for that computer.. I build computers so that just sounds more like what I would pay if I where to deploy a Dual 2U
(but then again I might use semi used parts)
85 sites would be fine on either box long as they didn't wrong cpu intesive scripts, mysql etc. and a 16 player cs will probally do fine..