Planning, budgeting, and shopping are all important when it comes to economising on food, and not all of those is possible when you are working full-time (or worse, running between two or more jobs that pay by the hour). Getting supermarket bargains relies on being free at certain times of day, and it is very often the poorer areas that have no access to cheap markets selling off fruit and veg at the end of the day (assuming that you are free then to buy them at that time).
I don't think you can make a decent meal for anything like 30p; but I can get several meals out of a chicken, and know how to bulk things out with pulses and grains. If I had to, I could plan for a week, making sure that what I had left from Monday would be used up on Tuesday, and so on.
I think that children should be taught this sort of thing at school. It would be good for them later in life and they would learn or consolidate other skills along the way (eg arithmetic, proportions/fractions, creative thinking and so on). Obviously the whole ethos of the National Curriculum would have to change to accommodate it, but it would be great if they could do it for real - plan a few meals, budget for them, shop for the ingredients, cook them and show how they would use the leftovers for the rest of the week. They could do it in groups, to allow for BOGOFs etc, and learn co-operation at the same time.
My children were taught separate things like 'chopping skills', for an hour a week. These weren't much use really (they would have picked them up along the way anyway, as I was a firm believer in collective responsibility for chores), and meant that they came home with a bag of sweaty chopped cabbage or something, that parents had to think of a way to use. I don't think they ever brought back a whole edible dish, other than a traybake of Krispie cakes or similar. They were probably typical of their generation (born in the early 90's), and it's not fair to blame young people for not being able to do what no-one has taught them to do, any more than it's fair to blame older people for not being able to operate the latest technology or find their way around social media.