We live in Europe and rather north, so same things that tend to be cheap here may not be cheap there you live. And other way around. We also tend to have rather expensive food all together but especially many unhealthy things are more expensive around here. Then again also fresh veggies are expensive especially at winter. And many also at summer because they are shipped from far away.
When my difficult child moved out from home I worked with him to come up with healthy, inexpensive ways to feed himself. With him the problem is that he needs lots and lots of high quality food. He is a pro athlete with shoestring budget and his biological age is two - two and half years behind his chronological age. So he is just finishing gaining height (he got only about an inch taller during the last year) and starting to quickly develop muscle. He is also in process of building the muscle base for rest of his sport career. Few years from now (around 25) he should be physically in his prime and from there on it is more keeping it up and taking care of the body. But this rather intense training period he needs a lot of protein to build the muscles. He also needs a lot of energy to keep going. His daily intake is between 5000 and 7000 kcal depending the day. Of course he mostly keeps himself going with carbohydrates and he doesn't need to be afraid of fats (and needs high quality fats) but still he needs also lots of protein and that of course tends to come expensive. Here are some things we worked on his diet.
First, and most important thing, is to eat seasonal. This is of course mostly true with fresh vegetables but also with other things. Products out of season are expensive. For example cucumber price can be up to four or five times 'the summer price' during the winter. And because it is shipped from far, it is not even very good. So you eat whatever is in season. Same goes to fish etc. Around here fresh veggies are cheaper during summer, but most are expensive at winter, except root vegetables. So instead of lettuce it's much cheaper to eat for example grated carrot during winter. Also frozen veggies tend to be affordable around here and grate way to keep on budget and still get enough veggies. But also root vegetables can be used in many ways. My personal favourite is to cut potatoes, carrots, beetroots, rutabagas, parsnips and other root veggies to sticks spice them with marinade made of oil, garlic, salt and herbs and cook them in an oven. They make a delicious and in-expensive side. Also 'mashed root veggies' (potatoes, carrots, rutabagas and some spinach to give it some colour) is very good. Also soup made of root veggies is tasty, cheap and healthy. You can add goof fats with a little bit of veggie oil and add protein with cottage cheese. It also makes a good lunch to take with you to work, if you just have an access to microwave. You can save a ton, when you use root veggies to up your daily veggie intake. Lettuce can also be replaced by cabbage or bok choy during the time it is expensive. And while fresh tomatoes may be expensive, crossed tomatoes are excellent in many dishes and very affordable. Also with fruits the one that are in season tend to be cheap. Also canned fruits are good especially in cooking and deserts etc. My difficult child also uses a lot of berries, but if you buy them, they tend to be expensive. We are avid wild berry pickers and our difficult child has a free entrance to our freezers so they come free to him. But I'm sure one can also find some affordable frozen berries even if you can't pick them yourself.
Getting cheap fibre is easier. Around here they don't even really sell low fibre breads (we tend to prefer darker breads around here, for example I very seldom eat anything with less than 5 % fibre, usually we have breads with much higher fibre count) so the price of high fibre bread is low. But if it is expensive locally, it is easy to bake buns using whole grain flour and adding some brans (oat brans are extra healthy.) brans can be used to many other things also. They are grate in smoothies, with yoghurt and in porridge. I really don't know about your shops, but around here also whole grain pasta or dark rice is not much more expensive than white one. And is healthier and tastes better. Different kind of porridges also make a cheap meal. And when asked local school children which school lunch they like the most (we have free school lunches for all), barley porridge tends to be very high in the list right after meatballs and beat lasagne, pizza etc. easily. So it is not like kids would always hate that kind of food.
Affordable protein is a tough one. Around here we have tons of different kind of sour milk products that help with that. The best one (and the base of every sporty person's diet around here) is quark that comes virtually fat free and up to 10 % protein and is cheap. It's usually used in smoothies, eaten with berries or (canned) fruits (pineapple being a local favourite) or even eaten as it is (it's also used in lots of not so healthy baking...) Natural yoghurt isn't quite as good with protein but it will do. Cottage cheese is also a good one. Other than that beans and peas tend to be affordable and can be used in many dishes. They are especially good with minced meat foods like lasagne etc. Minced meat is also affordable (I know you have that pink slime thing, but you can get minced meat without it I assume?) and can be used to almost anything. And while chicken breast can be expensive, chicken thighs are much more affordable. They can be cooked in oven and after separating the meat you can use it to make pasta or many other things. Ham tends to be affordable around here also. Eggs are also cheap and high in protein. Omelettes with meat and veggies make a good dinner. Liver is also cheap and can be used to many dishes. Nuts and seeds tend to be expensive that so nutritious you don't need much. Have you tried making smoothie out of fruits (in season) and yoghurt. Mix some nuts or seeds and some oatmeal brans and take it with you to work as a lunch in thermos bottle. Easy, cheap and healthy.
Fish is often the toughest one. Having fish dish two or three times a week (and different fishes) can get expensive. But at least around here there are seasonal things also in this. Just now herrings and sprats are cheaper ones around here (and herrings are to die for anyway.) And many of our supermarkets sell salmon in great price to lure customers at times. Maybe you too have fishes that tend to be cheaper when they are in season?
Different kind of soups tend to be cheap, also paella, risotto, different kind of pastas, many baked dishes (especially from potato and meat/fish) etc. are easy to make also cheaply and from whatever is cheap at that moment. Old cook books can be very good in finding affordable recipes. They didn't tend to waste even cheaper parts of meat etc. in old times...
