They are two separate issues, your desire for time off session to process, and payment for a session. You can proceed with things dealing with both at the same time or separately. You can give notice today and say "I'm canceling this upcoming sessions for reasons I will explain at session on ____ . " You can then address the policy directly in person at your session, or you can wait until he bills you for it, if he does. If he does, you can ask to discuss it. But, ultimately, you can decide whether you will pay for it or not. Personally I think it would be worth paying for a session if that is what will be best for you (canceling). If you go just because you have to pay for it then you're not taking care of yourself and valuing your own needs. If therapy is worth paying for, then it's worth paying to not go to session, if that's what is best for you..

Sometimes you can play chicken with someone and their own policies, as in put them in a position to defend it and request that you follow the contract. Personally I think this is a contract that too heavily favors the therapist. I'd like to see what happens if you just cancel and let him raise the contractual issue of payment.