will be on monarch of the see in oct from L.A. to Miami via Mexico, Guatamala, Costa Rica, Panama, Colombia do you recommend vaccinations, esp colombia (yellow fever) is it worth getting as the inoculation costs £50 / $100

I don't believe any inoculations are required so I personally wouldn't bother with it. But it is really a personal choice based on your own health.

The cruise line should list the requirements or ask your TA. On our upcoming cruise on Princess we are required to get the Yellow Fever vaccination. We are visiting 3 ports that require it: Tobago, Devil's Island, and Barbados. Now we've been to Barbados before and never had to have it, but not Tobago or Devil's Island. On our itinerary, it states that the vaccination is required.

You probably will not need shots for your cruise we have done those ports several times and never need them.
Take a good bug repellent with DEET.

Required & recommended are 2 different things but check with your doctor.

Devil's Island & Brazil do require proof of YF shots