Beans, beans, beans. Nourishing, filling, versatile and very cheap. The cheapest way to buy them is dried. You then soak the required quantity overnight and boil then next day. Black eye beans and lentils (lentils don't need pre-soaking) are the quickest cookers, needing only about 30 minutes. They can then be used in casseroles, soups, pasta sauces, curries, chilli, pasties, salads - you name it!