If those monthly expenses include an all-you-can-eat buffet, that doesn't seem like a bad deal. If they also have good health care on board, could be a great way to spend some of your retirement!
Cruise ship that plans to sail around the world every 3.5 years, carrying a combination of buyers and renters. According to this newspaper article some folks seem pretty happy, others are not.
At $100-320K plus monthly expenses of $3K - $7K it's a bit too expensive for my taste and I get sea sick. You can travel the world and live in very nice hotels and apartments on that budget. That said, it's not crazy unreasonable either and apparently many Americans spend more than that in dreadful land based homes.
What I find encouraging is that isn't a libertarian sea steading project. At least that wasn't the perspective of the people they interviewed. And the marketing doesn't emphasize that either. This is just a mainstream option now.
https://www.nrc.nl/nieuws/2025/03/28/geen-thuis-meer-op-land-maar-wonen-op-een-cruiseschip-a4887727
Discussion
The thing about retired though is that you have plenty of time for cooking, and really all these other chores they do for you. Or course some people hate those. But you can probably hire a decent personal chef plus cleaners in most of Europe for much less.