Among other things it will depend on your sailing resume, whether you have every owned a similar boat before, or havelogged hours on it. Or have taken a boating safety
course or other formal training
. And the age of the boat. And the survey
. And the sailings water
that you are asking coverage for.
All of that before deductibles and limits are mentioned.
You might try calling Al Golden at IMSI, 1-800-541-4647. Catch them when they are not very busy and he'll gladly explain some of the variations--including the ones in poilicies that you'd never think to ask about--and he might even give you some ballpark figures.
Mind you, between this year and next year those numbers could change wildly, if there is a lot of storm damage this coming season.
I suspect that a lot of companies here "I only need liability" and to them it sounds like "I have no concern about my own losses but someone said I have to get this stuff" which sounds like a much greater risk than "I've got this really valuable boat that I'd like to insure and protect and take great care of...."
Al and IMSI are not the cheapest--but they are top-line pros and old-fashioned gentlemen. And often very competitive.