Just get PC with top of the range PSU, Xfire motherboard and shove as many 7990s in it as you can. I wouldn't bother with 7950s they're crap!
At this point $/kh/s the 7950 is actually the best scrypt mining card. At around $300 for 650+kh/s they are tough to beat.
And OP yes IMO that is quite over priced. You could probably source those part online for about half what he is charging you.
Edit: ugh I don't like single fan cards, I have a Radeon ref design 7950 and it runs way hotter than my dual X 7950's and 7970. Actually I burnt out my first ref 7950 had to RMA it, I'm assuming when OC'ing it I cooked the poor bastard. Luckily for me it was inside the 30 days and I returned it to the place of purchase for an immediate replacement. If I was outside that 30 days I would have had to RMA it back to Sapphire and while I'm sure it would have been taken care of it certainly would have been a PITA. So now I don't OC the replacement card and it runs cooler but also barely breaks 600 kh/s but has been stable and running for me for months now.