I have a single gentleman who wants to do a cruise out of LA/San Diego area to the Mexican Riviera and I've been watching for quite a while - except for a couple of the 3-day cruises on Carnival, no one has been offering any good single supplement tours for this itinerary.
But to answer your question about Princess, they occasionally offer a decent single supplement, however they are far and few between.
Then again, it's not just Princess. Many years ago we use to see alot of really good deals for singles - we're just not seeing them as much anymore. Celebrity was one that was very good for singles, but now only offer them very rarely.
And many times when single specials are offered, they're for the unusual itineraries, such as those shorter or longer than 7 days, one-way repositioning cruises, or those very early or late in the season.
NCL came up with some single cabins on the Epic and it seemed to be popular enough that others are starting to pick up on the idea. I know there are some really nice ones on the new Quantum of the Seas. Hopefully, this trend will continue and make it easier and cheaper for singles to cruise.
__________________ Travel Agent/Cruise Specialist w/12 yrs exp and 47 Cruises on 11 cruise lines! Favorites: Paul Gauguin - Tahiti: Uniworld River Cruises - Europe; Celebrity Solstice-class ships; Holland America - 12-nights Baltics & Russia; RCCL - 14-nights Greek Isles, Turkey, & Croatia; Holland America - 14-day Alaskan cruisetour; 10-night Canada/New England cruise; 21 days Hawaii w/7-night NCL cruise; Oceania - 25 days in Asia; more than 3 months touring Europe by train. And many all-inclusive resorts!