Hi there, again
If you haven't picked up the Pardey's Cost Conscious Cruiser
and Annie Hill's Voyaging on a Small Income
, you might do so now. Both talk about budgeting, etc. Both focus on ways to voyage with only the income one can make while voyaging--so they are quite focused on smallest boat possible and recognizing the sorts of things that can break your budget if you're not careful. If you will have a nest egg, retirement income, etc, you can evaluate your own situation differently, of course.
Further, the link I gave you earlier to the Bumfuzzle adventure is good because that couple included a wonderfully detailed budget for everything they did as well over a four year period.
I've read in several places that you won't spend less than what you spend on land for food, alcohol, eating out, etc. Some folks budget about 30% more than their land-based food costs. We're still in the US, and can't speak to what other folks do here or internationally. We do happen to spend less when we're staying on the boat for extended periods but that is because there's no eating out
at those times.
When you get a boat, a good surveyor can assist you in understanding the maintenance requirements of the particular boat. Many folks throw out numbers stating that if you do a good job keeping up with your boat maintenance (sails, engine, hull, systems, everything) that you'll spend x percent of the boat's initial purchase price in maintaining it. I've heard 5% frequently stated, and I've heard numbers from 3% up to 10%, so I think it depends on the boat size, materials, fit-and-finish and expected state of condition throughout your ownership of it. Also, if you're a DIY type person vs having everything done by professionals.