"what if calories cost money.. would it change peoples eating habits?"
For the most part, i think it would. A lot of people don't eat as healthy as they should because of how expensive eating healthy actually is. Take lettuce for example: 2-3 bucks a head of lettuce while it only have 7 calories per 100 grams! granted salad would be alot more once you buy the dressings as they are unhealthy but eating better would be one hll of a lot better. people would stop going out to eat and cook more home-made meals.