Rob,
you're talkin kinda crazy here bro!
instead of buying a generator or some such, just pick up a couple more batteries from Batteries Plus or somewhere. ya got time. mouser.com has some great deals. just get yourself enough battery power to do a three show run. then use the power invertor to charge while driving to the next town.
otherwise, i've got some extra batteries ya could borrow. but once you pay shipping on those, ya might as well buy yer own. hehe...
lemme know if ya need the extras. could give them to ya at Alpine. you'd just havta ship 'em back. BTW: what ya need? 6V or 12V?
peace
~S