If you have a Lidl, they usually have £1.99 boxes of veg near the till which are coming up to their end of life but still value for money. You could make soup with some of the veg and a stock cube and freeze some for another time. Much cheaper than tinned soup.
Turkey mince is cheaper than other meat. Batch cook a Bolognese sauce, you can have it as is for spag bol then add a tin of chilli beans to bulk out and make a chilli.
Beans on toast is an ample lunch. I also like whole tinned tomatoes on toast.
Or baked potato with beans.
When I was a student, I used to make a sausage risotto: chop up sausages, fry up with onions, add rice, tinned tomatoes, herbs & spices (whatever you've got) and a stock cube, add water till cooked. A pack of sausages could just about do 6, especially if you can bulk out with some veg (where the Lidl box could come in useful again).
Tuna, sweet corn and pasta with a white sauce, either direct from the pan or if you have any leftover cheese you can grate some on top and bake.
Tesco and Asda and probably other supermarkets sell 'cooking bacon' very cheaply which is just bacon off cuts but exceptional value for money. Can be chopped up and used with pasta, or eggs for an omelette. Sometimes you get proper slices which you could have in a sandwich.