Check out free or low cost food in your area. Things like Olio where people give away ay food. There are some 'pay what you can' markets popping up around the country.
I've just checked Olio near me and within a Km is someone with excess bread and bagels, and also about 100 eggs. Don't worry people will split amounts.
Allotments often have a 'shop' that is actually a shed but with cheap veg.
Meal plan.
Do not be scared of tins and frozen food. Beans on toast is perfectly acceptable as a 'meal', for hungry children add extra toast and fruit.
Use a milkman (or woman) so you are not popping to the shop midweek, lots deliver bread and other bits.
Frozen fruit can be blended to make a smoothie, or to add to home made yogurt.
I use a local butcher, I pay about the same for meat but it is much better quality and almost always pennies are knocked of the final amount or you will get an extra sausage.
Look for older recipes / cookbooks.
One of my 1980s books has a sort of lasagna made with pancakes.
So you could do pancakes one day and then with left over pancakes layer them with passatta and veg (or meat) and top with cheese sauce, with bake them or freeze.
The same batter can be used for yorkshire puddings which can be filled with meat / veg or eaten cold with golden syrup.
Buy onion salt and garlic salt, these are not strong enough to make something like garlic bread but can be used to add a bit of flavour.