The highest tier with a price on it is burstable 8x4Mbps with guaranteed 1x0.5Mbps for $9k a month, which feels about right for a ferry (especially with some aggressive caching). They would break even with 30 customers paying $10 for access, though really I would be surprised if a ferry went far enough out to sea to need specialized internet (I am out of my depth, though, so maybe they do).
All in all, interesting. The markups still feel high, but not nearly as outlandish as I would have thought.
I wonder if at huge economies of scale you can get cheaper marine satellite internet if you don’t need full-ocean coverage. Eg cruise ships seem to sail the same routes on repeat, they don’t really need coverage of the entire ocean. I wonder if Royal Caribbean et al get cheaper service because they have pretty static and pre-defined routes, making it easier for the satellite provider to ensure there are satellites overhead when the ships are there.
In that context it's a rip off, and higher latency/lower speed.
On the 4 or so companies I checked, most were metered as you said but also clearly designed for personal vessels. They were also expensive as you said; I think the cheapest I saw was ~$1500/month for 5GB, and $0.39/MB for overages.
I am in no way an expert, this is just based off like 4 links. Someone said Inmarsat had more commercial-vessel sized plans so I checked them out, and they do seem way cheaper if you’re planning to use the link a lot.