The cheapest meals are meat free, so there need to be a few meatfree meals to offset expensive meat meals.
Soup is cheap. Pasta is cheap. Rice is cheap. So in a week add a risotto with leeks and mushroom, a tomato, red lentil and carrot soup, and a pasta with a spicy tomato sauce. or any other rice/soup/pasta dishes.
We have decided to like and eat a lot of pumpkin. They serve for two meals per gourd and make a good meat substitute. Meals like a pumpkin risotto, a pearl barley pumpkin stew, a pumpkin and spinach lasagne, a pumpkin laksa, roast stuffed pumpkin- all cheap and filling meals.
As others have said dried or canned beans and pulses are cheap and filing, dhal, chickpea curry, butter bean burgers, Cannelini and tomato casserole, mashed white beans with thyme and butter (served with fish or meat) all,work and taste great.
Bacon and sausages are some of the cheapest meats, bacon can be used very sparingly so a pack covers two meals, a carbonara one day, a fried bacon and pea risotto the next. Sausages make a million meals, casseroles, meatballs, toad in the hole, with mash and gravy, with roast veg, sausage rolls, hot dogs, the list goes on if you google.