We just did the pride of America.
We were thankful to rent cars on each island -- the excursions through the ship are very expensive. For example, in Hilo, we rented a car for $75 and we drove to the volcanoe park -- it's very easy to get to -- drive straight! The gas was maybe $25. To have booked through the cruise for 3 people would have cost around $300. Just grab a map. The islands aren't that big or confusing to get around. You can drive from one end to the other in a couple hours.
The cabins are the smallest I've ever saw in my life. Literally only room for your legs around the bed to move. The bathroom is like it was designed by NASA or something -- squeezing people into the smallest spaces imaginable. There is also very little storage space for clothes other than a closet. That's it. You're in the same room for a week, but you'll still be living out of your suitcase the entire time.