I have never been on a cruise but friends and family who do cruise a lot say to never pay for the cruise line's shore excursions. That you can always get together with other cruisers and take local taxis or other transportation to see local attractions. My cousin says taxis come to the docks on every cruise she has taken. When I picked her up when her Alaskan cruise stopped at Astoria OR, I did see several and there were hundreds of cruisers walking off the ship and dispersing in all directions. Towns where cruise lines stop are ready for tourist dollars and make it easy.
Some people like to play it safe and take the shore excursions but there are options. Do research in advance for sure.
I got a brochure for a Hawaiian cruise and was appalled at the prices they wanted. Must be how they make up their profits. No way would I pay them. You can even rent a car in advance if you are going to be in port over night or for a long day. Which is what we are going to do in Honolulu and Kahalui Maui if we go on this cruise.