I just found a shop that is clearing out old stock, I have not built a mining system yet but have the opportunity to pick up a number of these cards at $550 a pop( potentially less if I buy multiples). Is this a decent price for setting up my first mining rig? Or should I stay away from these older cards and get something like the newer 290x's?

edit: its the Gigabyte GV-R799D5-6GD-B 6G  Model

OK I just measured the power through my iMac with a 6750 chip in it.

iMac not mining:              72 watts.
iMac running DiabloMiner: 88 watts.

So turning mining on adds 16 watts!  Whereas mining on my 5850 adds about 150 watts.

The iMac is not using much power for the graphics card!

The the electricity to keep the iMac on all day mining is only $0.34.  Whereas the 44 MHash/second earns you $0.85.

So the iMac is still profitable as a miner.

Sam