Junk food and processed food are cheaper than healthy foods as they contain such a lot of fats and sugars amongst other things. I much prefer paying extra for good food and paying less on other things.
I tend to make things in batches when I've got free time and freeze them. Eating healthily involves quite of bit of vegetable scraping, but plain frozen veg. is just as healthy. There are practical foods like cheese and yoghourts which need no preperation. Good luck to you both.