You're not factoring in costs in attention, logistics, and (for many people) willpower. "I'm hungry. The bananas are black and we ran out of oatmeal Tuesday. D

You're not factoring in costs in attention, logistics, and (for many people) willpower. "I'm hungry. The bananas are black and we ran out of oatmeal Tuesday. Do I want to do some chores (cook) and then eat rice and beans in an hour or do I want to get a double cheeseburger on sale?" Drinking water and eating less is (for most Americans) much healthier and much cheaper, though.