You're falsely assuming a 1:1 ratio between calories and cost. Unfortunately the big problem with ultra processed food is that calorie rich but nutrient deficient food is way cheaper than the less processed foods. Cutting out the cheapest items is going to reduce spending less.
Not falsely. Back of the envelope. If you want to improve the model go right ahead, but I was upfront with its limitations.
I hear this a lot but I really don't see good evidence for it. And people keep peddling stereotypes about "fast food" consumption after QSRs saw much larger price increases than grocery stores. For that matter, the UPFs are where I see people most commonly reach for overpriced name brands over the generics.
It's perfectly fine for people to do rough estimates to understand a situation, especially in informal discussions. It not a dissertation for a Ph.D. or formal position paper.
How much is a bag of Doritos? Compare it with a bag of white rice, dry lentils, raw potatoes - processed is often more expensive.