The cost depends greatly upon whether your son needs laser, plastic surgery, or both. If the hemangioma is fairly flat, you can probably go with just laser, and that should be considerably less expensive than plastic surgery. Depending upon the size and exact location, laser might be a 30 second in-office procedure. Plastic surgery will require GA.
Also, I don't know where you live, but there are other doctors that are very skilled in treating hemangiomas. Dr. Waner is great, and he has seen my youngest, but we traveled to CA for her two plastic surgeries. We are only two hours from NYC, but the other doctor was in-network. You should consider that there are some other great doctors that might be covered by your insurance.