I'd say that's about right for that size and year boat. Many insurers won't even touch a boat over 15 years old, so getting anything at all is a positive thing in my mind. Did you let them know of any lay-up periods - If you only use your boat 6 months out of the year, for instance, there are discounts for that.
For reference, I pay nearly 3X that for my '95 Cafe (but that includes the Florida rape-me surcharge).