Juice is not healthy food though, it has just as much sugar and as many calories. But with regard to "it's cheaper" that's outright wrong, Americans dont purchase most things by weight, and processed food kind of markets around that but like if youre looking at a 2.50 bag of chips, and 2.50 worth of fresh produce, the produce is sold by the pound so you can get a few pounds of food while a bag of chips is what, like, 15 ounces? It's all WalMart math, where it just looks cheaper on the surface--kind of like how people from other countries say they were surprised at how Americans dont apply tax until the checkout because tax is included in the prices where they live. It looks cheaper, but you just have to think about it.
Even accounting waste, pound for pound, fresh produce and food and making it yourself is cheaper every time.
Capitalism doesnt work on tiny margins, in the big picture, McDonalds wouldnt run their dollar menu stuff if it cost them anything significant, even if youre looking at a 20 dollar/wk grocery bill and saying "Well its cheaper to buy the dollar burger, dollar fries, and dollar drink, plus tax, each meal, because its only a few dollars," I mean it comes out to a significant amount and the deal swings in McDonalds' favor, you know? Even if you only eat the dollar burger and get water, youre looking at 14/week on two meals a day, or 21/wk on three, not including taxes.
The only reason to rely solely on that sort of food is if youre homeless and have no means to actually cook for yourself, which some people do.