I guess I'd assume that the premise driving this would be that there will eventually be enough business in space that it's necessary for space-centric use, and that terrestrial use is just a fringe benefit or loss leader or something.

But oddly this doesn't seem to be how the concept is typically framed.

My second level curiosity is how much cheaper/competitive it'd be if we had space elevators.

Space elevators are pretend, you may as well ask if it would be cheaper if we had dilithium crystals

space-elevators require various types of unobtanium and have their own logistics challenges not to mention failure modes that involve spattering fast moving debris round the entire equator