Insurance from a legitimate marine insurer will run you about 1% per thousand of agreed $ valuation.
i.e. if the *Agreed Value is 75K, you will pay approx $750. per year. At 100K, you will pay approx. $1000/year.
Seems obvious, but be sure that the proposed purchase will actually pass a survey. At least 95% of boats over 30 years old will have deck delamination because no past owner has
ever re-bedded
all (!) of the deck fittings. They just allowed it to deteriorate, and allowed the value to fall until it finally went into free-fall. (sigh)
*If the insurer will
not agree in writing to the value, walk away.
I presume that the normal cost of docking/mooring a boat of that length has been factored in to your future plans. And, when traveling to other marina's and YC's, the limits on where to dock and at what cost.
"Good luck storming the Castle!"