So I did some research the past few days and have created a small matrix of card price vs mhash.
The mhash speeds were taken from the hardware matrix here:
https://en.bitcoin.it/wiki/Mining_hardware_comparisonPower draw figures were taken from here:
http://en.wikipedia.org/wiki/Comparison_of_AMD_graphics_processing_unitsPrices are generally before tax/shipping and most of the prices came from Newegg.
This was compiled during the first week of June 2011.
Card | Price | Speed per $ | Speed | Power-draw
5770 @ $95 = $0.44/mhash 215 108w
5830 @ $110 = $0.36/mhash 300 175w
5850 @ $200 = $0.64/mhash 315 151w
5870 @ $500 = $1.25/mhash 400 188w
6750 @ $100 = $0.60/mhash 165 86w
6770 @ $95 = $0.52/mhash 180 108w
6850 @ $150 = $0.65/mhash 230 127w
6870 @ $165 = $0.55/mhash 300 150w
6950 @ $220 = $0.58/mhash 375 200w
6970 @ $310 = $0.82/mhash 375 250w
6990 @ $750 = $1.00/mhash 750 375w
Given the results of this data and shopping around for a few days, I am buying a few 6870's since the 5830's are no longer to be found :-) I chose the 6870 over some of the lesser cards mostly due to possible resell value and re-purposing for my gaming rig.