I don't know how else to understand "When comparing things like bread and butter, the ultra processed versions are much cheaper.", other than as a claim that ultra-processed versions of things like bread and butter are much cheaper than non-ultra-processed versions of them.
A loaf of white bread here costs a minimum of $1.99 (all prices CAD) and contains by my reckoning a bit over 400 grams of wheat. So nearly $5 per kilogram.
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.