Once you are at anchor in the Caribe, all you really need to do is eat and do laundry which costs about double what it does here in the states. You can do passive stuff for electrical needs when you outfit your boat. So...you can get by really cheaply.
On the other hand, most people don't do that and Melrna's #'s look reasonable except you CAN go higher in the pricier areas, staying in marinas and paying very high prices for electricity.
A lot depends on how you live and what your other expenses are. Health Insurance, Boat Insurance, boat repairs etc.
If you are on the move, you need to account for customs/immigration fees and fuel for boat and dinghy.