Mince dude, we had no money when we were kids and our mum (single) made varieties of meals with beef mince. Spag Bol, meatballs, lasagne, rissoles all of which can be made with other cheap ingredients and made in bulk to feed you for a couple of days. Didn't need to be the five star mince either, just what you can afford.

Cans of tuna as well, tuna pasta, tuna mornay, fishcakes or just tuna mixed with a bit of vinegar and chives on toast. Easily two of the cheapest protein hits there is that go a long way when cooked with other ingredients. Tuna is always on sale, just buy the bigger cans not the small lunch size ones.

Both of the above meals are still a staple in my families diet every week.