Some things are a lot more expensive, but if you stick to basics and plan it's still possible to eat well. Also to buys loads of tinned tomatoes or pasta when it's cheap.
Porridge is brilliant value, all ours love it with a bit of honey.
Home made soup is very cheap, if you use lentils and frozn veg with a home made stock. With some nice home made bread and cheese it makes a lovely healthy meal.
Baked potatoes with tuna or cheese or beans with salad is also cheap.
Macaroni cheese is cheap but not so healthy.
Anything to do with eggs, eg Spanish omlette, normal omelette.
Stews with plenty of beans.
Frozen fish fillets, frozen chicken pieces and frozen veg are all good value still.
Home baking can be cost effective if you only eat it instead of puddings.
Cheap puddings are custard and tinned fruit, milk puddings, natural yoghurt with jam or honey stirred in.
Basic popcorn popped in the microwave with a bit of toffee sauce stirred in makes a good treat.
Will stop now. Getting hungry...