Portal Store rented them last year for $2 each (easily the best deal). Unless it has changed from last year, there is one size, it will fit in your backpack, and has sufficient space for a two-day food supply (actually, for three or four, depending on how much you bring). While sleeping overnight, *never* keep it in or near your tent. I put mine on the ground next to a large tree and buried it under a bunch of rocks I'm gussing at least 50 feet away from our tent (and the campground). Although bears can't get into these containers, they are not smell proof, and you don't want a bear nosing around in your tent at night looking for it.
CaT