I don't remember the price, but it less expensive than going through Carnival. I saw the tour on a ParoDeeJay video. If you search Youtube for the ParoDeeJay channel and then search for Amber Cove, you should find it.
We went up the mountain to the botanical garden, saw the statue of Jesus, visited a Rum factory, cigar shop, city center, fort, and had an authentic Dominican lunch.
We were the only people signed up that day, so it was like a private tour. You do need to walk outside the port area to meet the tour. On the way back, there is a cab waiting that will drive you back into the port for a few dollars.
Mike