After a bunch of research, I've decided on using A123 Lithium Iron Phosphate batteries. You can discharge them at 35C (35 times their rated capacity in Amp hours {AH}). I'm gonna buy 160 3.5 volt 26550mAH cells to start off with. The cells cost about 20 bucks each from A123 systems (yikes!). I did a lot of shopping around and found that they are used in 36 volt DeWalt battery packs. These packs are $150ish each on eBay and have 10 cells, so $15 bucks each (still yikes!).
So after browsing around for a long long time I found that certain 28 volt DeWalt Batteries (DC9280) also contain LiFePO4 batteries. I found a website that is selling these packs (8 actual cells per pack) for $49.88 each, with free shipping. That works out to $6.24 per cell. Bought 20 packs of them (160 cells total).
