carrots and cheap and filling,
other veg varies, you can just go to the supermarket or green grocer and see what is cheap today.
Bananas is another go-to for me, when skint..
Porridge with full fat milk is a cheap and filling breakfast. Big cartons of natural yoghurt, with any cheap fruit is a good dessert. raisons go well with either, and can sometimes be brought cheaply
sausages - well, some are better value nutritionally than others.
eggs, a bit expensive, but a good source of protein
Cheese - massive differences in price - look for multi buy offers as it lasts
Rice, particularly brown rice, is much better for you then pasta - can be flavoured with onion, spice, etc.
lentils can be very cheap
Don't forget green leafy veg, lettuce, cabbage, etc very important for a healthy diet