Ask the locals in the Carribean what they eat. They are experts in low cost living in the area. They certainly don't need $1,000 a month
Correct but maintaining a modern vessel , basic insurance etc has a base cost more or less dependent on type and size of the vessel. Food will cost what they are paying now more or less. Most people seem to find costs are lower than land living given that property taxes on the average house in the US can keep some cruising for 6 months. No car is also a big savings especially if loans are involved. The OP has 130k capital monies for said vessel. They should have little problem getting a well found vessel bought surveyed and upgraded for that the is good for a couple.People spend what they have generally but given the y have the capital I doubt a sea life will be more than a land one.
Just my 2 cents