These are always difficult cases. Present your data to the carrier -- if that does not work, you can pursue a lawsuit against the person who damages your vehicle. You'll need counsel to maximize your chances of success. Look for someone that has successfully prosecuted diminished value claims.
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.
Show them the comparable and ask for the fair market value based on what you found.
My name is Stephen R. Cohen and have practiced since 1974. I practice in Los Angeles and Orange County, CA. These answers do not create an attorney client relationship. My answers may offend I believe in telling the truth, I use common sense as well as the law. Other state's laws may differ.. There are a lot of really good attorneys on this site, I will do limited appearances which are preparation of court documents it is , less expensive. However generally I believe an attorney is better than none.
Your policy provides for the insurance company's choice of repair, replacement or total. When the insurance company totals the car, it buys it at a price that is determined by a data collection service. For example one provides the prices at which cars with similar age,, condition, mileage and features have actually solid for in the 22 western states to arrive at "ACV" or actual cash value. Unless the carrier is blatantly wrong you are not likely to get more than a small adjustment from your own carrier. DV claims can work, but many carriers will fight a DV claim tooth, fang and claw... get a lawyer with a successful track record in DV if you go this way.
Your best bet is probably to put together as much evidence as possible (i.e. kelly blue book kbb.com, nada value (nada.com), ads from craigslist or the newspapers, repair estimates, etc.) and send them to the claims adjuster and tell him why you should get what you should get. It can be hard to find an attorney for whom it would be worthwhile to work on that kind of situation.
As a last resort, small claims court does work. See link below.
[In accordance with the Avvo community guidelines, this communication does not constitute "legal advice", nor does it form an attorney-client relationship.]