Subject has also been covered quite a bit in previous threads on this forum. When you have a couple of hours to kill you can read this thread about cruising on a budget
. Just click on the link below.
Cruising on $500 / Month
At the end of the day, it will depend on you. If you shop at the local markets, cook on board, buy hamburger instead of filet mignon (or for the vegetarians brown rice instead of imported wild rice) you can live pretty cheaply. Basically food costs will be roughly similar to what you spend at home if you're willing to adapt and adjust your food preferences to local brands.
All that being said, if you are shopping
at a super market and buying
prepackaged, prepared foods instead of local produce, some Caribbean
islands the cost can be double what you would pay at home. Same for toiletries and such.