Well I guess it depends on where you are in the Caribbean. Last year coasting through the Bahamas the price of bread was around $10US. BVI, which has an official currency of the US$, is very expensive and one of the highest mooring rates in the Caribe. Marina Del Ray in Puerto Rico is the same as US prices. But once you leave BVI and hit St. Martin and further south, the costs are reasonable. But why are you thinking of using a Marina. 5 seasons in the Caribbean and we have only used a ball of a slip no more than 10 times. Your anchor, set proper, will hold for free better than a rickety dock. Even the ones made of concrete. You'll have less damage and save tons of money.
Cruising Budgets are not talked about, and even before we left we tried, as you are, to determine a budget. We have a 41 foot modern sailing sloop and could be considered upper middle income. We do not scrimp if the boat needs something, but we do not over do it either. Eating ashore, once south of St. Martin was a 40/60 situation. I imagine if you want to live well, think of $2,000 a month. (without fixed boat expenditures like insurance) Frugal and you can get by on $600. Biggest learning curve, water costs almost as much as diesel in some islands. Other islands it's at the fuel dock for pennies.
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