Well...paying for your health insurance and boat insurance for all ocean coverage can be $10k per year...unless you decide youand the boat aren't worth it! After that...you need to BUDGET about $5k annually to cover normal maintenance AND unexpected breakdowns and bank whatever you do not spend towards next year. I would budget after that, your expenses for food, drink, cutoms/immigration, marinas, fuel etc. which largely depend on your own choices and lifestyle.
The above numbers are ballparks for 40'+ cruising boats and couples in their 50's. You can go "barebones" camping for $1000 a month in a smaller boat ith no insurance or live it up.