Apple has an architecture license. I don't know what the terms of the license are but it allows Apple to develop architecture compliant chips. They were one of the original developers of the original ARM and held a large stock position in ARM Ltd.
Do we know what Apple is paying? Remember that ARM started as a joint project from Acorn, Apple, and VLSI. Apple certainly held a full architecture license from founding, despite not designing one until comparatively recently, which to me implies there's some specific license.
I certainly assume they weren't paying large amounts for a license when relatively poor in the 90s despite holding one.