It is estimated Apple Pay does anywhere between $5T to $10T transaction per year. That is everything from Credit Card to Debit Card. If we average out at 0.1% per transaction over $5T, that is $5B per year.

The transaction itself doesn't touch any Apple severs. In case anyone is wondering if there is an operational cost. There is a set up cost though with the initial verification and sometimes Apple do charge a one time fee per card set up.

There is a privacy angle with using Apple Pay. But I am unsure how much info banks and network is not getting because of it.