The problem you are running into is that all repair shops go to their computer to develop estimates. Many commercial software packages exist to develop estimates for 'normal' cars. Too bad there is nothing 'normal' about a JH, which means 95% of all shops will want to charge actual time and material.
For budgeting purposes, most of my clients spend $3k-$6k getting engines rebuilt, and there are plenty of stories of T&M jobs exceeding $15k. The last time I got a painting estimate, it was $4k for a total job, $500 for a 'slap job' at Maaco.
Then there are plenty of club members who can tell you how much money they have sunk into total restorations (a friend of mine recently spent $70k on an A-H 3000 restoration).
My suggestion is print out the JHPS marketplace showing the value of 'typical' cars, and the NADA blue-book value. This information will show it will be easier for the insurance company to give you replacement value instead of actual repair cost.
Given the option of haggling to pay you $15k to get it repaired, they may just 'give' you $5k-$7k to buy another car.