Try Sam's Club for pricing, and they have different options for house/coach batteries, including deep cycle, and dual purpose, in both FLA/GEL/AGM. Not sure if they sell lithium yet, but they probably do. Some of their brands like Duracell, are actually made by battery companies like East Penn and Trojan. I started using one of their dual purpose AGMs as a chassis battery a few years back, and it's been better than a typical starting battery, as it takes a lot of abuse and still works. Something like that would probably work as either chassis or coach for you.
