In short: pretty much blue book UNLESS you can show greater market value.
"Actual cash value" as used in insurance means what the item would sell for in the market that exists at the moment of the loss. That number is determined by whatever items of similar age/condition are actually selling or at least advertised for.
We ran into this after a tree jumped in front of my Husband's pristine-condition 1978 Ford heavy half. Insurance company averaged selling prices and made us a lowball offer. But we were able to nearly double the settlement amount by proving that other trucks in the very unusually original condition were selling for higher prices.
We've since gone to an "agreed-value" system for those items we think would otherwise be undervalued.