Low- or zero-prep junk food is also incredibly cheap. When I see comparisons done it's usually ingredient costs of healthy food to full-price junk food costs, but that's not how poor people shop for junk food. They go to Taco Bell when the tacos are like 60¢ each or less, through promotions or coupons. They buy Totino's frozen pizzas eight at a time, on sale at half-off. They buy giant bags of store brand sugary cereal and pairs of 3L bottles of store-brand soda, again, on sale. Costco pizzas (they are so cheap on a calories-per-dollar basis, for zero-prep hot food) and bakery items for the enterprising slightly-less-poor who can scrape together the annual fee. Whichever chips or snack crackers are on sale. Off-brand pop tarts—holy crap those are calorie bombs and very cheap and you wouldn't believe how many kids have a couple of those for breakfast most every day. And so on.

Even relatively-healthy-but-not-really-healthy frozen meals can't compete with the outright crap. It's so very cheap.