lol, 12s is a bit much. I test-fitted two of my 14-cell NiMH packs for weight/size, and it's a bit unbalanced. And I would need to dial in tons of shock preload. 28 NiMH cells is roughly the same weight as a 12s/5Ah pack weight-wise. Besides, that would be spinning my 1515 Neu to over 73k rpm!
As far as lipo price, I would need 10s @ ~5Ah, which would be ~$600. But I have ideas to keep it well under $600.