What's important here is calories. You're not going to be sitting around in a TEOTWAWKI senario, you're going to be very active dealing with security and other tasks.
Solar oven = zero fuel. Spend as little as the cost of a roll of foil or a few hundred for a store bought oven.
You make a good point. I'm with ya when it comes to having some ready to eat (or easily made editable) foods on hand. I keep those in totes incase they need to go with me in a bug-out.
On the other hand, I think it's far cheaper, healthier, tastier and offers serious variety to have basic foods in bulk in your food storage (e.g. flour, cornmeal, sugar, spices, flavorings, oil, beans, canned meats, powdered milk, powdered eggs, canned butter, canned & dried vegetables & fruits).
Just my thoughts and what I've done...
brick rocket stove