Pros and Cons.
Cost of out fitting down there and so on?
The real problem is I don't remember seeing any good boats for sale there. You certainly do see boats for sale there, but as we used to say, they look like they've been "rode hard and put away wet". I suspect many of these are boats owned by absentee owners who have gotten tired of having to manage a boat so far away. A lot of people living stateside seem to keeps boats in the Virgins. They hire someone to look after the boat for them. Some of these arrangements don't work out so well and the boat ends up in bad shape.
Another problem would be making sure you're not getting a hurricane damaged boat. It's amazing what horrendous damage can be repaired so as to virtually invisible. We knew a couple who decided to retire and go into the charter boat business. They flew to St. Thomas and bought an existing charter boat. No one bothered to tell them the boat had been blown ashore by Hugo and a hole big enough to walk through had been bashed in the side!
Another problem would be viewing perspective boats. If the boat is really a "good deal", you may have to act quickly. That could mean lots of trips to look at the "good deals". Could get expensive unless you work for an airline. If you peruse this I suggest you find someone you can trust who lives in St. Thomas. They could look at a boat you were interested in first and let you know if it's worth your time to come take a look. There are plenty of yachties there who would do this for a little money. I'd make a trip down and find someone. The two of you could look at a few boats for sale so they would get an idea of your likes and dislikes. Then you would have to make future trips only when your agent said there was something worth seeing. I've found houses and, in fact, I bought "Down Time" this way.
As to your refitting question, I think it would be the same as here. I don't remember supplies and yards being any more expensive there than stateside. There is a do-it-yourself yard on St. Thomas (Independent Boat Yard) if you are so inclined and there are a number of full service yards in both the British and US Virgins. Shipping from the US is not particularly expensive and of course there are no customs hassles as would be true in a foreign country (we are planning to talk about this in a later article). All trades are available and there are many cruisers willing you work to replenish the cruising kitty. It's even legal for them (the US ones, anyway).
In summary, I guess my recommendation would be to buy stateside.
The person who asked these questions lives in Seattle. If I were in the market for a boat specifically for this type of cruise I would look in Florida.
There's a big difference in boats intended for warm weather cruising versus those intended for cold weather. You'll find boats built in cold climates that don't even have opening port lights. Can you imagine that in the Caribbean.
Remember that one of the things you get in buying a used boat is all the after market equipment the previous owner has added. Florida boats are more likely to have stuff you need (like a bimini) than a Seattle boat which may have stuff you don't need (like a heater).
Just our thoughts.