I’ll never know the answer to the question because the AI writing is such a turn-off.

"Cheap enough" doesn't exist as an isolated term, it's "cheap enough given task involves some specific competence".

I can vibe code a card game on an unpaid Claude account, so it's definitely cheap enough to replace developers (and businesses selling card games) if you just want a card game.

A whole modern operating system? Right now, I think you'd still need to be a developer just to direct the AI well enough to make more than a demo.

It's simply not possible to answer this question with authority at this point in time.

The most obvious reason --- almost all AI vendors are currently operating at a loss and are carrying huge debt and other "future" obligations.

Current prices are no indication of real costs --- and even more so looking forward.