I am still surprised someone is dropping 2500 and doesn't even know what hes shooting for. Some god trust hes putting in you guys. Dont get me wronge, you are all good people, and very well educated in more than one area. But jesus, I'd probably kill for a computer like that! (watch out archanix...).
As far as building it. Best Buy would probably charge you a lot, considering you'd never buy those parts from them, and I think you may be better at CompUSA, they charge less for builds usually, and most of the time you can get a nice warrenty if you dont open the boxs before they do.
I work at CompUSA as Comp Tech, and build em all day. I'd sya 1/15 computers have at least one part not from CompUSA. That part can't be OEM or it doesn't get any kind of warrenty.
Before you buy this stuff, check out with he local stores, definatly safer than sending it to someone else, and having them do it for even half the price. Even if they do everything perfectly, they can't gaurentee a $2500 50lbs built kickass computer wont get messed with in shipping...
Just my 2 cents. Spend your money well, I wish I had it.