Message in a bottle
Its sounds like finances are your key consideration. I don''t want to get into the medical insurance issue, as it varies for everyone, but rather the issue of boats and cruising costs.
I think that having a good plan, considered well in advance, is the key to limiting your cruising costs. I don''t know if you already have a boat but your choice of boat can dictate your later expenses. A nice large more traditional boat like a "Capt Ron" Formosa 51 might be compelling. But... being a 1970''s vintage it will need a lot of upgrading and most systems will begin to go. You want to spend your leisure life in leisure and not working on the dinghy outboard, replacing through hulls, bilge pumps, tech decks, rigging etc etc. Of course, if you have had a boat for a few years prior to cruising and have already upgraded all systems before going, you should be OK.
Also, in my experience, I have found that marinas have a somewhat common slip arrangement. 40ft slips are standard and may accomodate a boat up to 44ft with no extra cost. Of course most places will charge by the foot. Once over 44 ft....you then begin to pay big time. Again...this is in my experience, obviously this is not true everywhere and if you are going to be anchoring in the south pacific, it does not matter.
But in general, the bigger the boat the more everything costs. The older the boat, the more everything costs. I am not sure what the perfect boat size is...and LOA does not relate directly to cabin space or comfort...LWL and displacement are better indicators IMHO. And different people have different needs...this would be an interesting thread on its own.
After that, your cruising costs can and will be adjusted by how often you eat out, how often you take a mooring or slip and where you cruise. The islands are not cheap anymore and fresh water is not free anymore. But by and large, many cruisers are out there doing it.
Hope this helps.