Not only did he get the year wrong, but some car dealer's value is always gonna be jacked up so they can get you to come in and trade up to some more expensive car, whose price will be more than you'd pay with no trade-in. I think probably the most reliable estimate would be the Kelly Blue Book value, which takes into account all the options, condition, etc. The value to a private buyer will be higher than the trade-in value on their website and you could take the average of the two prices. It's a reasonable, objective basis for value that any court would probably accept.
What an idiot. Sorry it has to be such a painful exercise. I was lucky that the only time I had to divorce a drunk we had virtually nothing to divide.