To clarify: of course there's a cost to using the facilities! I assume Seabourne factors costs like these in to excursions. My astonishment is at the cost being added at this late stage, for a luxury liner. Especially if this has been common Icelandic practice for 10 years, you might expect it to be signalled in a general statement as part of information about excursions.
(Sorry, looks like I can't get the quote functions to work on my tablet.)