A 2600K, mobo, and 8 gigs of RAM can be had for $450. A couple creatively wired OCZ ZX1250W ($150 each) could power 10 builds, right? Is this viable, yet?
$180 for six hyper 212+
You could probably power 3 or 4 rigs with a decent 1250 PSU, but I can't speak to the quality of that particular model.
So you're looking at $3060 for six CPU, mobo, ram, and cooling. Then say two PSUs at $300
That probably puts you around 450,000 PPD (75k * 6) for $3,360