Ditto on MaxAmps, I've been using them in the Slash 4X4 SSC LCG truck for some time. They cost more, but really supply the power the Castle ESC and motor need. And provide plenty of run time. 20 minutes for the smaller pack when racing. I use a DuraTrax Oynx235 charger, which is balance only for LiPO and LiFe, for all the battery packs, NiCad, NiMH, LiPO without a problem. A nice feature is the battery terminal clips, lets me charge packs when out in the boonies. It's not the most expensive charger, but good enough, and helped offset the cost of the MaxAmp packs. I consider a balancing charger a requirement for LiPO and LiFe packs for every charge.
I've only bought one used rig, a T-Maxx the kid next door had for sale after he graduated, dirt cheap, after completely rebuilding it a new one would of cost less. But I know every screw, nut, gear, etc. after the rebuild. Besides, it was fun.