Having owned twin turbo diesels , shaft driven boats for 36 years ( 150 Hinos (4000 HRS ), 270 Cummins ( 1200 Hrs), 330 Cummins (2600 Hrs) . These are hours I've put on, not total engine hours. I totally disagree. Other than normal maintenance, they have never cost me a nickel. Spent more on repairs for my outboards and I/O's than the inboard. diesels.
Old rule of thumb from when I was in the boat business 45 years ago were - to be comfortable financially, the boat should not exceed 10% of your net worth and one should budget !0% of the boat's value for annual maintenance and upgrades. Some years more, some years less, but fairly accurate over the years at least for me.
Hope this helps. Ted