I make pizza once a week: Cheese tomato and sweetcorn and I only use mozzarella, I don't use cheddar on pizza.
The flour cost 80p for one 2ilb
The yeast cost 99p for one tin
The cheese cost 44p
The tinned tomato cost 37p
The frozen sweetcorn cost £1,50
Dried herbs to sprinkle on top £1.00
I use 11oz of flour and one teaspoon of yeast, all the cheese and half the tomato, one table spoon of the sweetcorn. To make one pizza. Next week I will have to pay 44p to buy more cheese - everything else I will have to make a cheese and tomato pizza and that will be the same the following week. So for three weeks I will be able to make pizza by only replacing the cheese and tomato.
So I agree if you make a particular dish or meal and buy all the ingredients it may be expensive the first time at £5.10 but add another 88p for the mozzarella and 37 p for another tin of tomato and you have another meal and so it goes on as you will not have to replace the flour, yeast, sweetcorn or dried herbs.
I buy a couple of kilos of potato, I will not use all the potato for one meal but for three or four meals.
I will make a tuscan bean soup
cabbage 80p
boroti beans x2 50p each from the world food isle or 70-90p else where int he supermarket
carrots £1 for bag
stock £2 for whole packet
tomato puree 38p
onion 50p
garlic £1 for puree
tinned tomato x 2 37p each
I will get 10 portions of soup for £7.40 - buy soup and it is £1.50 per portion.
Added to which I make the soup again the following week and I will not have to buy the garlic, carrots, stock, tomato puree or the cabbage. As all these will be left over to use again.