Minced pork is cheap and delicious mixed into balls with soy sauce, garlic, sesame oil, and some reconstituted dried mushrooms (these are not super-cheap but you only need a few and you might have some lurking at the back of your cupboard. If not, use normal ones cut up very small and fried, and a glug of worcester sauce). Poach them and serve over a bed of cabbage with chilli sauce.
Pasta is really filling with creamy sauces and parmesan: someone has mentioned bacon and courgette; smoked salmon off-cuts and fried leeks (with a few capers and some lemon juice instead of the parmesan) is also nice, as is roast butternut squash with sage, or broccoli and garlic.
Cous cous with roasted veg and chilli sauce is a good way of using cheap market veg that need using. Onions, courgettes, tomatoes, aubergines are all really good here.
Sweet potato and savoy cabbage hash: steam everything til tender, then fry. You can crack eggs into this and bake til they're done. Also good with bacon or chorizo bits. Other hashes, eg corned beef, are good too. Leftovers are really good for breakfast / weekend brunch.
To make a chicken last 3 days, even for a big family, try roasting then stripping some of the meat off for a pie with veg (frozen peas, carrots, leeks, and whatever needs using) with a puff pastry top and baked potatoes on the side, then use the rest of the meat the following night (with broccoli and mushrooms in a garlic cream sauce in pancakes? Once they're assembled scatter with cheese and bake); then make stock and do a veg risotto.
Also pancakes with anything in are good too.
Hope that helps!