Login in to the web based Cruise Personalizer and then click on Manage this Booking. Then click on Check-In. Scroll down and click on Dietary Requests. You will then see where you can select Distilled water for CPAP.
You should be able to see the cost of the Princess coverage in the Cruise Personalizer. I think you can buy it directly from Princess.
https://book.princess.com/cruisepersonalizer/index.page?cpfy=insurance
Did you try clicking on "Site Feedback" at the bottom of the home page and then in the popup select the "The Princess Cruises website team" and click Next ?
Yes and it is still inexpensive. I take it you shop at places that over charge. Princess will be purchasing products wholesale and have contracts that were set a long time ago.
Princess does have a master chef at HQ and he is relatively new to the line. I have seen his cooking demonstrations on Youtube and do not look forward to sampling food that is prepared in his style as he takes great pride in those videos of serving burnt food.