Well, my first thought is that 80C isn't bad at all... I usually get cranky if my GPUs are regularly breaking 100C. They're designed to run that hot...
If you want to look at a pre-done 4 GPU build (which won't break 2GH/s on stock clocks), I have a quad nVidia build for other purposes detailed here:http://blog.cryptohaze.com/2011/06/quad-gpu-builds-with-case.html
I have the board/case/PSU/etc listed. I got all of this plus a 6870 for right around $1000 shipped.
You're not going to be great on cooling, but the Antec 900 pulls plenty of air through the side window once you remove the plexiglass & as long as my garage isn't too hot, I don't have trouble keeping them cool.
If you're looking for the most cost efficient way of doing this, I'm probably not of much use.
But you said budget wasn't a concern.