Here is what I will do. I jsut orderd 80 x 6970 to be delivered in slices over the nxt 4 weeks, as initial step.
6970's are not anywhere near the best hashrate per $. Trust me, I have some so I know.
Right now the best hashrate/$ is the 5830's at newegg. 286 MH/S for $130. Around 2.2 MH/S per $. 6970's do around 380 MH/S for $320, so they are only 1.19 MH/S per $. Of course, you have to consider the price of the motherboard, power supply, etc because you will need more of them per MH on account of the lower powered 5830's.
Check out
https://en.bitcoin.it/wiki/Mining_hardware_comparison The price/MH column is wrong because people don't update it when they update the card prices, so you have to calculate on your own.
Anyway, as I have said in other threads, right now the ROI on mining is the lowest it has ever been, less than $.01/MH/S/Day. If diff increases grow at less than 1% a day, you may be able to get more bitcoins over the course of a year than just purchasing them outright now. But based on historical data, you will get more bitcoins from simply purchasing from the market.
Good luck.