I can't imagine it being cost effective to pay someone to do this repair. Shops around here are $100 an hour and up. And this job will likely take two workers, not one, so double it.
I would start with any local marine shops. Someone proficient in repairing fiberglass boats should be able to handle the trailer.
Best thread I have found on Burro
floor replacement. I can see a professional charging somewhere in the $5,000 to $10,000 range. Its one reason so many of these repairs are do it yourself.
Project trailers are best suited for someone with the TIME, tools, aptitude, covered work area to undertake such involved projects.