If you go to 'ports of call' on the Thomson website and click on each port at which you call, it will list the excursions with prices. Website address: http://www.thomsonbeach.co.uk/th/cruise/viewPorts.do.
No matter who you cruise with tours are always very expensive,my advice to you is do them yourself it is so easy and far cheaper,we have done the caribbean for the last two years and have always done our own trips it is just so easy.
I agree with Streets Worksop,ship organised excursions are quite expensive,we have just returned (Jan 19th.),from two great weeks on the Destiny in the Caribbean everything about the ship was excellent from Sevice,Frendliness of all the crew,entertainment,food and destinations great.
It was no problem doing the sites and beaches by yourselves ready available taxis/minibuses at all ports of call.
Leaving the ship their are loads of people doing the same things so you just agree to join up with them and share the transport.Much cheaper than paying for ship organised tours.
Every port of call also have tourist information desk where you can check details of cost and places to see.
Finally the amount of information you receive from onboard destinations services makes sure you can not go wrong.
Have a great cruise I am sure you will.