If the market rate for dirty jobs goes up, will the basic income be enough, or will I struggle to pay for my waste collection (and everything else) on the basic income alone?
With a basic income, now most of these people have more money. So I can charge $3 per apple, and even if I only sell 4 of them I still make $2 more than I made before. I eat the last apple myself, and the person who only has the basic income doesn't get an apple at all.
I think universal welfare makes more sense.
Your $12 in case B has a purchasing power equivalent to $8 in case A.
In general terms, UBI seems sane. I see two implementation problems. First, worldwide society competition: Can my society support UBI and compete with China? Second, automatic system balancing. What is the correct UBI level? Can we leave it out to be hashed by politicians?