Cooking bacon is a good bet. Cheap and can be used for soup, bacon and onion roly-poly, quiche, carbonara sauce etc. You won't be able to afford any ethics, I'm afraid - no free range eggs; you'll have to buy the "concentration camp" ones.
Lentils, rice and pasta plus tinned tomatoes for sauces, soups etc. are filling and healthy.
Supermarket "own brand" sausages e.g. Sainsbury's basics, can be used make meatballs andsauwage meat patties as well as fried or put in a toad in the hole.
Batter is your friend - pancakes, yorkshire puddings etc - filling and delicious.
Cook in quantity whenever you can - freeze the excess to have a quick meal later. This goes for rice etc as well - It's as cheap to cook four portions of rice as one, and freeze in single portion bags for use with curry, stir fry and risotto..
Chilli can be made without meat, as can curry and many pasta sauces. The BBC Good Food website has loads of brilliant recipes. Baked potatoes are delicious and nourishing with leftover pasta sauce, cheese, curry or just a bit of butter/non-dairy spread.
Your greatest enemy will be boredom - if you can learn to use these cheap ingredients in a variety of ways to keep yourself from getting jaded it will help you massively.
Tinned fruit can be quite cheap (pineapple, peaches especially) and will give a lift to many savoury dishes as well as cakes and desserts.