So I have very limited income and I have to ration what I eat all the time, but at the expense of trying to stay thin.
Most food that are cheap and in quantity always have ether too much carbs or sugar.
But if I have a way to plan a meal a week in advance that is both grounded to the goals of my budget and my health.
Sometimes I wish there was an app that took all the ingredients on discount from my local groceries and also showed the meals that I could make with it that takes my dietime into account.
I feel you pain on trying to get food on a budget, I suffer the same here with a drain of a brother that doesn't care about budgeting and controlling his urges at all.
Being completely honest we haven't been able to purchase as much food for the money that we expend on it, so we end getting less while paying more for it. Potatoes, onions, carrots, sweet potatoes, tomatoes, cabbage, Chinese cabbage and the occasional daikon radish or eggplant comprises of the brunt of the vegetables that we purchase.
As for meats, we normally get discount or sale chicken pieces, more often legs and sometimes breasts. Then sausages and very few times pork and ground beef. Eggs are relatively cheap here in Brazil so we try to always have some around, we pay 10 bucks for a pack of 30 chicken eggs, it doesn't last long because we eat it a lot.
Then we get bread, rolls that last a couple of days, 2 packs of sliced white bread, some cookies and pre-made toasts. I always ask for 2 kilos of flour so I can bake more bread, make pasta or when I feel like a pie or a cake. I consider that we crossed a emergency threshold when I begin to dip deeply into my flour supplies to cook. Like making something like chicken and dumplings with more dumplings than protein.
Another staple is bulgur wheat for kibbeh making. It is very filling and nutritious. It is another of the borderline items that I use when there is nothing else to use or I want to stretch the pricier proteins. I have two main recipes with this that I use that fills you up good. It is a cheap food that we can buy in a wholesale food store nearby, I always ask for 1 to 2 kilos of it and it is fairly cheap for the amount. Since you need to soak it to use it, a little bit goes a long way.
Pasta and rice are staples here, it stretches proteins and is pretty good. Here in Brazil the standard plate has rice, beans, salad and meat. Rice and beans are a perfect pair according to the medical professionals, they complement each other nutrition. Bean also stretch well and can be purchased in bulk cheaply.
Now alternative stuff, I advise that you buy nutritional yeast. Powder and flakes if you can, the powder is good to make spreads or to add to breads before you make the dough to add extra nutrition to it. The flakes can be used to sprinkle on foods as if it was parmesan cheese. It is hard to believe but it does help to fill you up, or just give you the sensation of being full earlier and for longer. TVP if you can ger cheaply is also a good way to get protein on your diet if meats are too pricy. My issue with it is that is pricy here and I can't get a good flavoring on it when I cook it. But it isn't bad and if you make heavy sauces as curry or tomato sauces the TVP will get its flavor.
I don't know what kind of diet plan you are following, but as long you aren't eating a lot of fat and oils, eating the regular staples should help you lose weight. Hibiscus tea, green tea and the home made gatorade helped me to lose weight while I ate what I mentioned here and some occasional fried food.
Don't be afraid of canned stuff, canned corn is a common thing here, we use it for many dishes and it is cheap. Fritters, adding to sauces, making cakes, mixing with rice and other vegetables for a fried rice dish, and more uses. Canned sardines have a fairly strong flavor that you can use considerably little to make a lot of food. Flaking the sardines on some tomato sauce makes for a nice pasta sauce, and this is just one option.
If they are cheap canned tuna or other fishes can help to get more protein on the cheap, check the net for recipes and you can use the same canned stuff in different ways.
My final advice is that you purchase the ingredients rather than purchase pre-made meals, the initial cost might be a bit higher, but with a bag of rice, a bag of beans, some vegetables and a meat, you can get more meals that when you tally the total cost each meal costs far less than the factory stuff. It just takes time and effort.
Cooked beans freeze well, so when we have leftovers we freeze them to use another day. Rice can be repurposed into fried rice if you add vegetables and a bit of protein, meat or eggs to it. Leftover vegetables could be turned into soup, pie filling or used in stir fries with the rice. Same with meats, mix with the vegetables to make fillings or soups.
I don't know if this will help, I hope that it does even if just giving you a basic idea on how to start a new way to help stretching your budget.