OK this has been a thoughtful discussion - just few more things to add -
Nature and Science are obviously different than the journals discussed but see:
This is showing there is some push back on Plan S as it was rolled out.
Geoff gave some great example of taxonomy journals that offer OA inexpensively but for many journals the OA cost is more like $1500-$3000. Fo Nature Communication it was $5200 last I checked a few years ago.