Yes, the Disney excursions include taxes, but not gratuities. If you're going by this year's prices, expect prices to slightly increase next year--add 10% to your budgeted amount, just in case. Also, Alaska is very easy to do on your own, so you can save money that way; especially if you have a kid in the 10-12 age range that pays adult prices for Disney excursions and kid prices on outside excursions!
In 2016, we did 2 excursions on our own--Skagway--Chilkoot Charters Yukon bus/rail with dogcart ride--highlight of our trip! Juneau, we bought tix for one of the Glacier Express buses in advance (could easily be done that day--Disney shuttles you from port to the area with all the port excursion companies at the start of town.) It was $30/person roundtrip--buses came every 1/2 hr to take you to/from Mendenhall Glacier visitor center. If you wanted to do Mt. Roberts Tramway--I'd decide that day as you'd want clearer weather to actually 'see' things from up there! The Tramway starts right near where Disney shuttles drop you off. Ketchikan was our 1
DCL excursion--Saxman Native Village and Lumberjack show. Lumberjack show is in walking distance of the ship--so again, very easy to do on your own! But, I did like the DCL one we did here. For the Saxman Native village, they let us into the Clan house (with a performance by the Cape Fox Dancers (tribal kids)) and the carving shed--a lot of the outside excursions can only take you to see the totems on the property.
Enjoy your cruise!