I'm always browsing Ebay for a steal. This isn't necessarily a steal, but it's not a bad deal. I have a couple Z600s and they've run well so far...

HP Z600, dual X5650, 24GB RAM, 1.5 TB HDD, Windows 7 Pro 64 bit, dual Quadro FX 1800...$549 + +$65 shipping

http://www.ebay.com/itm/301794111323

Or keep your eye on this auction, but you'd have to upgrade the CPUs. If you got it for less than $350 (including shipping), would be good deal...http://www.ebay.com/itm/121811587387