First, I'll tell you right up front that I'm not a big proponent of shore excursions offered by the cruise lines. They are too expensive, too restrictive, not as nice, and always too crowded.
Talk to you agent and do some homework on the internet about the ports you're visiting and you'll find alot of options available to you. For example, the last time our son and daughter-in-law were in Key West, they wanted to go jet skiing. I found them a company offering a tour that went completely around the island, was about 28 miles, stopped at 5 places, and took about 1-1/2 hours. It was off-season, so they only paid about $75, but I know the price has gone up.