Yes, There are exceptions, although, it's worth pointing out that a pinto bean is processed minimally in terms of drying. Like I said, if all you want is calories you can make bread with a 5lb bag of floor and some salt at less than half the cost per calorie of pinto beans.
The point is, if money is tight, which invariably means that time is tight, people don't have time to cook dried pinto beans, or make bread for EVERY meal where the prep time is roughly 12 hours. Add into that, even knowing how to cook is a skill. An all bread and pinto diet is likely to take more time than most people have, and not yield a great health outcome anyway.
If you look at it as categories, the junk food, and processed food aisles are where you are going to on average get your dollar to go furthest.
The whole point of the "myth" is that it is FAR more efficient and cheaper to get everyone enough calories with food from the junk aisle. The origins I believe come from a cooking show where the budget and time were limited. Professional chefs gave up.
Here's the challenge: you need to serve a meal to 4 people (2,500 caloriesp) you have $10 and 1 hour including shopping and cooking. I can think of half a dozen meals that come from processed foods where that is possible, but doing that with fresh foods is HARD.
If you want to go the pure science route, here's a peer review study from the NIH showing that in many places on earth, healthy food is provably more expensive https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6825829/