Check out this site they got some good prices on the Lipo's as well and they got 9000mah 2s2p 35C 7.4v lipos for $50 or the 5000mah 2s 30C @ $27.08 - $34.09 and a 7.4V 2s 5000mah 40C @ $38.59

I dont know much about the electric stuff but came across these and thought I would share the info.