Probably not much because they still have to license the same Music for YouTube.

I know some people hate bundled Music. But I doubt unbundling it will reduce the prices.

This is what puts me off paying the Danegeld for YouTube more than anything else, I already pay a fair amount of money for Tidal which I'm perfectly happy with. It's bad enough Apple insist on incessantly hawking Apple Music at me with a popup every time I open the music app on iOS for my offline music collection, I don't want a third music service trying to crowbar its way to my life whether I want it or not.

What Youtube does is pretty much the infamous U2 album but with an entire streaming service, forced bundling like that is never not obnoxious in my opinion.

YouTube music is simply a different front end for YouTube. Removing it would not make it any cheaper.