I think that is a fair price for the work that was done 1/3 of the job is tear down 1/3 is stringer replacement and 1/3 is carpet , top cap and final assembly. So you are doing 2/3 of the work and saving 4k . The Michigan prices you quoted are ridiculous . Its a lot of work you should expect to pay 5k for the complete job . Pictures of the build are a must a lot of sins can be covered up with decking and carpet. Unfortunately most of the older Supras don't warrant a 5k stringer job especially if the rest of the boat needs work.