Having just had a septoplasty 3 weeks ago, I can speak a bit about this matter from the patient's perspective as well as the doctor's. First of all, many of the very best surgeons don't take medical insurance anymore because of the paltry reimbursement paid to the doctor. You must realize, though many patients don't, that your surgeon is usually only paid a small fraction of the bill by the insurance and the amount is getting smaller all the time as costs rise to do the surgery and run an office, pay staff and all the bills. Therefore, if your surgeon has the kind of reputation of being the best and has enough patients willing to pay his or her fee, they will thrive while working out of the insurance network.
Remember, however, that septoplasty should be an insurable "medically necessary" procedure and there are many doctors who will do it totally through insurance. They just might not be the best at doing it. All surgeons are different in their talent, skill, training and experience. Personally, I believe you should go to the best and hopefully only have to do the operation once. Revisions never get to the same outcome as a well done one-time operation!
I took my own advice and went to Dallas where the best surgeon for me happens to be located. He is a doctor's doctor. I had a very complex septal obstruction and he has resolved it beautifully in a complex surgery lasting 3 hours. Consequently, I am extremely happy I went that way and would do it again in a heartbeat. I paid up front for surgery and will try to get something (not much) back from my insurance after the fact. The facility and anesthesia are being billed directly to my insurance. The fees you describe seem high though and you might exlpore other options. The surgeon I went to is Dr. Jack Gunter. There are none better in my opinion. I hope this personal story helps!