> When comparing things like bread and butter, the ultra processed versions are much cheaper.

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.