I agree with Liz on this one - healthy foods are often more expensive than cheap fat filled sugar coated lard.
Many times I have been on a budget, and had no choice but to buy the cheapest on offer, unfortunately most cheap fruit is about to go off, and salads at £2.00 to last a day, yet a big family bag size of crisp for the same price (24 bags for £2.00, sometimes twice the amount if buy one get one free) is going to last a few more days in a sandwich, than the mixed salad will.
Not that I have gone to that extreme, but when I have had a tight budget, I have had to cut back severely on fresh fruit, and bought food fillers instead.
On the other hand, my children have been brought up with no fizzy drinks, very few sweets etc, because of my sons kidneys and then because of his hyperactivity. They only have water and milk to drink, and without much complaint. My daughter could get away with drinking fruit squashes, cordials etc but she has had to have water, and it won't do her any harm either.