This should probably be in the Ports section, but none the less I'll give it a shot.
Where does the Imagination dock in Jamacia? Ocho Rios or Montego Bay? The falls are very close to Ocho Rios but require about an hour and a half on a bus from Montego Bay. Resulting in the excursions price from MB being about $100 a head more than from OR. If you book as soon as you get on the cruise ship (book from your cabin TV is fastest) you should not have a problem.
As far as private tours.. I assume there are, but if you are docking in Ocho Rios, its a short taxi ride (about $10???) and the entrance fee to the falls is like $15. I think they want $80 for a ship booked excursion. Just be sure you arrange a return taxi and plan on being back long before the ship is to sail in case you run into problems. If you get a taxi driver that wants to do the "round trip" price, DO NOT PAY until you come back to the ship or he will take you money and not return to bring you back.
Anyone have experience with a private tour company and the falls?
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013