Why is my genioplasty so expensive? Two years ago I had major orthognathic surgery on both jaws to correct an overbite (Photo)

Even though my teeth meet, my bite is angled so my lower jaw still looks recessive. Originally, I was supposed to have a genioplasty during the main surgery, however, the surgeon changed his mind and said that I could always do it later. He deducted $500 from my bill. I now want the genioplasty, but my surgeon is reluctant to do it. I got two quotes from other surgeons which were both $7500. The original surgery was only $11,000 and that was 7 hours of major surgery. Is this a realistic price?