Changing the PCB for a known-good one: $10 + maybe half an hour of low-skill work.

Changing the failing component: maybe a few minutes, probably a few hours of an electronics engineer that's familiar with the design (plus his expensive tools). He's probably bad at soldering, so you'll need someone else to do that. Then you need to revalidate the board.

It almost never make economical sense to try to repair the board.

If you have a surplus of donor components, board-level repair can be very feasible and often even profitable depending on the board.

The fact that we tolerate creating waste because it's "economical" is frankly disgusting. The disposal fees for e waste should make it uneconomical to dispose of boards.

Also training techs to repair SMD parts is really easy and cheap, you're grossly overestimating the costs. The real waste comes from boards with designs that can't be repaired so we tolerate a certain yield. For many small devices the yields are shockingly low.

The other thing is that yields are low because of bad designs. If it became uneconomical for you to throw half your boards out then designers would fix their crappy boards with tombstoned jellybean parts because they used shitty footprint libraries. This is a solvable engineering problem and it's gross that it's cheaper to throw shit into a landfill instead of fixing it.