There are companies that will do a DV appraisal for you. It’ll cost you a few hundred bucks and they’ll give you a detailed report showing how they came up with the number. The insurance company of the folks that hit your car will try to lowball you. If they didn’t provide a comparable vehicle while yours was in the shop, claim some loss of use as well. It’s useful to have an additional chunk of money that you’re seeking to recover that you can discount (or not) as a negotiation tactic.