I've been a full time cruising live aboard for 24 years - and the critical 'cost factor' is "what does it cost you to live and maintain your happiness and current lifestyle right now? I mean aside from your home and car and on land associated expenses - what does your 'lifestyle, comfort zone, and happiness cost you now? That's what it will cost living on your boat.
For example - I consider my boat as my "travel and lodging". On average, (sailboat) it costs me near $7,000 a year. That's what I spend for ALL my boat, fuel and boat related expenses - including marina fees, canal fees, Permit fees, etc. HOWEVER - I spend 5 times that on me and my lifestyle. That's food, beverage, ice, toiletries, clothes, eating out, rental cars, and being a tourist at all the wonderful destinations along the way.
People that tell you that you can 'do this' on very little money and no income or huge savings are smoking seaweed. You can't live on the fish you catch, rice, beans and pasta for very long and be happy. It can be a very 'frugal' life on a 'frugal' boat, but leaving the US you need a Passport, if you stay longer than 90 days, you need a Visa, On arrival in the Caribbean you have $300 Entrance Fees, Cruising Permit fees, Fishing permit Fees, even a Departure Tax. Cruising America's Great Loop may in fact be a better option, it will for sure prepare you for cruising the Caribbean.