root veg soup is cheap
basic pattern of fry an onion, add the chopped veg (whatever is cheap and to hand) and sweat, add water, stock, season, blend and maybe add some cream or dairy at the end. add potatoes too to bulk out and garlic/bay as appropriate.
congee is very cheap - boil rice in water for ages until it breaks down and makes starchy soup and add anything you like. pork ribs/ham hock in with the rich for pork stock, add spring onion, cabbage, sweet soy, sausage meatballs, fish anything then, bit of nam pla and go
winter root curry (nigel slater korma recipe lovely)
pumpkin should be very cheap around here - you can then make curry, risotto, soup from one big one.
chickpeas cooked with loads of spinach, garlic, paprika, cumin and chilli flakes with olive oil - have with pitta and spoon of yoghurt and that's a nice meal.
cook big pan of bulgar wheat and add anything good to hand - roast veg, olives, capers, chopped red onion, parsley, chorizo, spring onion, feta, lemon juice/zest or preserved lemons and season and dress well
the key to me would be to find cheap market and buy what ever is cheap and then cook to that, keeping a few essential spices at home.