And now, if you allow me, I present you the best mag-for-$ GPU available on the market today:
http://www.ebay.com/itm/AMD-HD-Radeon-7970-3gb-GPU/292157192833
Yes, it's the HD7970 selling for $70 on eBay! Deprecated in the eyes of gamers and Proof-of-Work junkies, but hidden gold for Gridcoin miners, yielding up to 1.2 TFLOPS in FP64 (when properly overclocked). Point this classic GPU to Milkyway@home (a FP64 project) and you'll get to mag 150 in no time. 0.5$ per 1 mag, I dare you to show me a better deal, with any other device.
But hurry, because competition in Milkyway is getting rather strong :)
RE: Hardware and Project Selection Part 2 - GPU Projects