If you like solar panels you may like this, but it is ~$130. Expensive is different for different people so...

But, I plan to buy one of these soon:

http://www.xantrex.com/web/id/245/p/1/pt/32/product.asp

It holds a 10 amp hour charge. From one of your post's I think you will know what that means, and if it would work for you.

Cloudy? No worries, you can plug it into a wall outlet or a car's cigarette lighter adapter(maybe a ranger wouldn't mind you borrowing it for an hour?) to recharge as well. (presumably before you head into the bush/sticks/wild)

If you want to use AA batteries, you might consider these: http://www.thinkgeek.com/homeoffice/gear/8e82/
Maybe they could be used in conjunction with carbonLife's posted idea?
I also plan to get some of these, and then buy things based off of AA's (Lights for the bike...etc)