I would hate to submerge my food, only to find out it accidently leaked! Actually submerging a food bag is not that easy- they tend to float. A quality dry-sack will weigh as much as the gear needed to hang food.
I have a good roped hanging system, a Ursack, and several different bear cans. It all depends on where I go. Most of the Sierra either explicitly require a bear can or word the hanging regulations so difficult that you can rarely comply with the law. I mean, counter-balance it 12 feet high? Me? How to I get it down, I am only 5'4" tall. And of course, once above timber, you cannot technically meet those requirements either.