We have a reservation to go cave tubing in Belize. There are several companies you can book through. The price ranges from about $45 to $80 per person. The more expensive ones include lunch. I don't know if I'm allowed to mention this but there is alot of information on the cruisecritic.com message boards. You also may want to do a google search for Belize cave tubing.
We bargain down to $20/person for the cave tubing
Do NOT pay the price on the internet or the ship - the trip can be bought so much cheaper and we all ended up at the same place, same guides, doing the same thing.