I have been on the mexican cruise three times now, twice on the pride. As far as the shore excursions go, in PV we went this last time to the "Rhythems of the night" approx cost of $79 per person. Nice trip! You take a hour long boat ride to "Las Calentes" island for a very nice buffet style dinner of steak, chicken and fish with salad, rice, hand made tortillas and so much more and whoa what a dessert bar they offered. All of this in a romantic candle lit, sea side resort! The show afterwards is pretty nice also. We had a blast on the boat ride back and even got to see a whale!
As far as the other ports go, Mazatlan is my favorite to just catch a cab and have him take me on a mini tour of the city including their market place where I find the best bargains. In cabo, dont miss Cabo Wabo, but be sure to get there early or you wont be able to get in at all!