I just purchased 30 Tenergy, 14Ah NiMH āFā size cells from All-Battery Center on eBay for $335. If you can swallow/justify the cost, it should make a great pack, even though you will have to solder it up yourself. Total weight will be around 15 pounds and there should be power to spare.
Amondo Tech, also on eBay, offers some 12Ah āDā size NiMH cells. Thirty of those would run about $180, not a bad deal, although I've not read any reviews of the brand (Titanium). Again, these are individual cells. Total weight would be 12 pounds.
Andy