I think it's the same as "car
maintenance cost" or "house maintenance cost. It entirely depends on which percentage of
work you willing to do yourself and how smart are you while finding/replacing
parts. I'm also
learning about all of this. So far I found that many parts for
marine are STUPIDLY overpriced. But there are always ways around this. Engines can be rebuilt or repaired to new specs or replaced with better and less expensive engines. Cats can be beached, so hauling out can be avoided in many cases. All electrics,
electronics, mechanical systems,
interior - just
DIY. I bet many parts can be fabricated in mashine shop for less than new "original" replacement. Also, learn how to fabricate
fiberglass parts (that's what I do right now

)