For the most accurate numbers, you should ask whatever surgeon you are considering.
However, as a point of reference, Dr. O (probably the most expensive out there) quoted me about $11k for chin (genioplasty) and jaw together when I had a short consult at Southern Comfort back in Sept. My friend was quoted around $7k for chin and jaw by Dr. Spiegel last summer, and I'm not sure whether that is genioplasty or not. Price will vary based on what you need done obviously... I think genioplasty is the most invasive chin procedure, so it will cost more than others.