Don't know if you live in a town or not, but eating seasonally helps: eg today we had, amongst other things, summer veg soup (with runner beans from my boss's allotment, new pots etc) and plum pie (again plums given to us).
If you have a breadmaker, get it out & save yourselves loads of money whilst baking delicious nourishing loaves.
I also use lots of pulses (cooked in a pressure cooker for speed), & by liquidising the ingredients they can be well disguised in sauces - eg red lentils in pasta sauce - and soups - red lentils with carrots, onions & pots to make golden soup, split peas in with pots & leeks to make leek & pot soup; secret is not to use too many so that they don't affect taste.
Sosmix is cheap & makes good toad-in-the-hole or veggie sausages, and children can get involved by shaping them into whatever shapes they fancy.
My children like cheesy potatoes (layers of pots baked with milk & grated cheese), & sweetcorn fritters are cheap & easy (tin of sweetcorn, 6 tbsp flour, 6tbsp milk, 4oz - or less - grated cheese, mixed together & fried). My children love pancakes & baked potatoes, & we also use soya mince for bolognese sauce, shepherd's pie etc.
For a really cheap treat - or a money-making venture(!) - my children have had stalls at the school summer fair & in the street, get some popping corn & make popcorn. We have a popcorn maker, but you can do it in a pan, & it's far more fun & better tasting than what you can buy.
Bon appetit!