I am going to go against the majority once again. I key my food preps around high quality protein. Namely meat.
As long as one gets 60 grams of protein from meat while fairly sedentary, and up to 100 grams of protein or more from meat when very active, the healthier a person will be, and the more energy they will have, and the less they will I need of everything else. Of course you do need all the other things mentioned, to round out a healthy diet, but the core of the planning should be around sourcing that high grade meat protein.
Next most important in the diet is quality fats, like that found in coconut oil and nuts. It doesn't take that much quantitatively to get the calories you need from fats, but it is important to get them.
Carbs/sugars come last in terms of need. You do need carbs. Quite a few of them. But if your diet centers around carbohydrates, you will not be as healthy as you can be, and despite the low cost of the items, the overall cost of the diet will only be slightly lower than if getting your primary calories from fats and protein from meats with vegetables for flavoring, vitamins, minerals, and variety, fruits for the sugars, and comfort foods just to keep one happy.
For a 3,000 calorie diet for hard work in the PAW, 400 calories/16oz of beef/chicken/eggs, 2,250 calories18 tablespoons of coconut oil (or equivalent in other fats in other foods, and including that used in baking and cooking), and 350 calories 2 cups or so of rice/beans, and other Carbs/sugars, will keep a person working, healthy, and feeling good.
And the expense will be well worth it as you will be getting much more value per dollar.
Just my opinion.