That sounds about normal. My father always said that when he wanted to estimate how much a job in a boat yard would cost, he would estimate how long he thought the job should take to do and then double that. He would then multiply that number of hours times the prevailing yard rate. He would then add in the price of part and multiply the sum by two. And that would be the yard estimate. The job usually cost twice that. He first said that in the early 1960''s.
The other thing was our gag about a professional job. When I was a kid, Dad and I (actually mostly Dad but I did try to help) did most of the work on our boats. Occasionally he would run out of time before commissioning and ask the yard to do something for him. The work was really not up to the standard of quality that we would have done and so when one of us did a less than perfect job, the running gag was "You sure did a professional job that time".