Hi, Tom.
I am an orthopedic physical therapist and also a patient/survivor that had/has neck issues. After a neck dissection, your soft tissue anatomy is never quite the same. When you have soft tissue changes (muscle, tendon, fascia, ligaments, etc.), the joints stiffen up as well. You can also have referred pain from your cervical spinal nerves as well as your spinal accessory nerve, which must be physically moved out of the way during your neck dissection. Nerves are highly sensitive and they tend to hold a grudge when mess with them, no matter how gently.

Personally, I went to PT when I was about 2 months out of surgery. It's important to allow time for healing of the tissues before you start PT. In that time, one can certainly develop secondary issues, though. The swelling in the area can also contribute to the radicular pain (radiating pain in neck and shoulder). Since the pain is originating from your neck, doing the arm rotations will not do much. Be easy on yourself because you are so early into your recover. It's good to keep moving and to gently stretch, but nothing even close to vigorous. You could cause complications with your neck dissection that will only prolong your recovery. I would suggest GENTLE neck range of motion exercises. I can send you a PM with some exercises if you'd like.

I hear ya about the copays. Since I worked at the PT clinic where I got my therapy, they didn't charge me a copay, so I was lucky. After you're about 8 weeks out and your doctor is okay with it, you may want to go for a PT consultation only and tell them when you book the appointment that you specifically want to learn a home exercise program and cannot commit to a full course of PT. It helps the PT to know this ahead of time. It may take 1-2 visits to get it right.

I hope this helps and that your pain subsides quickly.

Take care,
Kerri