I am the allergic one in my house, I have every sympathy with the food bill regards HAVING no choice over where you buy certain foods/brands etc.
I am anaphylaxis to all dairy and also, since Christmas, tree fruits too (apples and pears mainly). Soya milk is sweetened with Apple juice, and apple juice is actually used as the basis for many juices or other things requiring sugar (so they can claim 'no added sugar'). It is bloody hard work buying food I am safe with, and if I go to a 'new' shop it can take me several hours reading all the labels to work out safety.....popping to another supermarket to get cheaper food is laughable!
I also have four teenagers and one nearly there......luckily the smallest (boy) is a picky eater and so does not clean my larder and fridge out, but the magically stretching boy (age 13, just grown out of school trousers #four since September!), could eat a whole chicken in one sitting, that once could feed the entire family.
I bake a lot (I have to, or I would be bankrupt with having to cater for allergies and the prices they charge for food that, technically, contain less in them than the 'normal' stuff), and one cake lasts maybe an hour after it is out of the oven.
I made drop scones the other day (scotch pancakes)....they ate them as soon as they came off the griddle....I was stood there for over half an hour cooking them, I got to eat 3. The rest filled all their very empty bellies!
I was once shocked at the stories my SIL told me of how much food her teens ate......at that point I had small folk who could share a happy meal between two of them and be full. I have been well and truly cured of my shock believe me...