It's interesting that overall spending doesn't decrease that much in the end, although shifting from snacks to fruit is the kind of change health advocates have always wanted?
Deserts are visible - obviously a pack of Little Debbies has no nutritional value and is purely excess calories - but what fraction of your total calories are coming from deserts? The real issue is excess calories in your regular food consumption, such as large portions. Indeed, if your meals were filling you, you probably wouldn't even be snacking to begin with. When comparing things like bread and butter, the ultra processed versions are much cheaper. In absolute calorie terms they have lower sticker prices, but they also genuinely appear to be better value: you can get significantly more volume of food, and it will last substantially longer meaning you can buy in bulk, reduce the amount of time you spend grocery shopping, and spread purchases out to better align with when money is available. More often than not they also require less time and effort to prepare good tasting meals.
I can't even fathom what you have in mind as "the ultra processed version of butter". Margarine is a completely different product from a different source.
Bread is a relative luxury regardless. The sponge-foam "wonder" stuff isn't even the cheapest for sale here generally. But even then, typical bread is (adding up the macros) only about 60% actual grain by weight (the rest mostly water), going by the nutrition label; so a kilogram of whole grain whatever equates to nearly two and a half loaves. Even whole rolled oats are much less expensive, on this basis, than the cheapest bread I can find and it's not complicated to cook them.
At any rate, bread and butter are two of the worst possible examples to make a claim about energy density in "healthy" versus "processed" options. Grain is grain (overwhelmingly carbohydrate and almost no water beside what is added in cooking or baking) and fat is fat.
Whatever it is you are trying to argue in your comment, it has nothing to do with the cost comparison I am making.
A kilogram of rolled oats can be easily found for about $3; white rice around $1.50 if you shop around; pasta from $1.33 to $2.22 depending (usually on the higher end of that); white flour $1 (in large bags).
A person can have a sandwich made of bread ate before your rolled oats are cooked. I think a huge portion of some people's confusion on why people eat what they eat need to look at time from picking the item from the panty to mouth to see that people spend a lot less time in the kitchen then they do.
I enjoy rolled oats uncooked in a bowl with milk and various berries sprinkled on top. Try it, for me they are more delicious uncooked!