If you order some from Hobby King, don't forget they have a US warehouse. I get my batteries in a couple of days where as others ordering from China take a couple of weeks.

Not sure what C rating you're using but here's a 40c 5000mah for $76: [link=http://www.hobbyking.com/hobbyking/store/__14986__Turnigy_5000mAh_6S_40C_Lipo_Pack_USA_Ware house_.html]Hobby King[/link]