Goal Zero. Their product is excellent but not cheap. Then again, I never install Radio Shack surround receivers for my clients, even if they say "cheap."

Remember that cheap might mean it gives out halfway through the trip, so if you do find something cheap you should try it out for several charge cycles. Fortunately, there's plenty of time now.

There's a Goal Zero charger on ebay with the bids at $23 right now. [Link: ebay.com]; three days left in the auction. Search ebay for used solar panels. Build one yourself and hope it stays together for your entire trip. I really recommend doing away with the idea "cheap," though.