you will have a limited time in Rome and it will take some time to see things that you want to see. Even that you want to burn the extra calories, after few hours you will be tired and probably not enjoying Rome as much as you think. Sooner or later you will need to find a restaurant which might be crowded and maybe expensive.
I would look at other option even if it will be more costly but maybe beneficial. I also would not pay the amount that you have mentioned either for the tour or the transfer to Rome.
We used a smaller company for the transfer that we were happy with and it was a lot less costly. Some posters ( here on CC and Trip Advisor) used that company for transport to Rome and a tour.
Write to them - it costs you nothing. Tell them what you want to do, see what they offer and than choose what you will do.
If you used them ( or some other similar company) - you will have more time in Rome, you will not be dragging your luggage at the port as well as in Rome. You will have a chance to see a lot more and have more energy. You might spent time in some nice family restaurant away from the tourist center ( the driver will take you there) - maybe even save some money on the dinner or lunch.