Wow, my whole fleet, 17.5 08 Tracker Crappie Pro, 16' 89 Panfish Special jet, and 15' Express little jet only cost me around $60 a year in property tax. 3 year boat tags are $31 now, permanent trailer license is around $70, forever one time.
I spend more money on batteries, tires, and general maint. than what you are worried about. They are all rigged like I want them. Screw the insurance unless the area where you go requires it.
The way I see it, less than one crappy rental boat.