Varnish work is not as easy as painting latex paint folks.
But depending on the condition of the wood as it relates to the grain, if the wood has been left to its own vices for a while can create double the amount of prep work before you begin to seal it.
And if you don't know how to use a hook scraper on small parts too, you can create a nightmare. And paint stripper can cause some serious damage on your painted or gelcoat surfaces.
So while your initial quote may be outlandish to someone not familiar with the going rate, hiring it out can actually end up being cheaper if this is your first rodeo, IMHO. But make sure to ask for references and then ask the boat owner was the job done in an expedited manner as weather permitted and even how long the job has held up. And ask what type of varnish was used.
There is some excellent sealers out there that can speed up the process before applying varnish. And by all means do not let anyone talk you into building up with epoxy either. And Epiphanes is twice as thick and a bit more expensive, but builds up faster in the process and holds up longer, especially in the northwest area of the country.. Make sure you get enough finish on your wood that it fills the grain.
This makes varnish last longer, as the varnish does not break down with the changes of temps and sun rays allowing the grain to crack the finish work that does not show a completely smooth surface.