Where do you plan to keep the boat?
If you are a US citizen, its going to be harder to flag it in another country, unless you set up a trust and pay attorneys for the rest of your life.
The charter companies commonly sell their inventory, but I would highly caution a new sailor from doing that. Those boats take a beating and you will pay for that in maintenance. If you're experienced, you can find a good deal.... maybe. They might, on the other hand, tip you off on where you can obtain financing down there.
Your problem is going to be insurance, even if you can find the financing. Insurance companies are not keen on taking the risk of a new sailor on a large boat. If you break it, smack into a dock, hit someone else, don't tie it to the dock properly, etc, they have to pay. They want to see that you've passed formal accredited training, have experience and no claims. While you can own a boat without insurance, you can't finance one without it.
If this is something you really think you want to do, I would spend the time and money to take a liveaboard or bareboat cruising course with your wife, instead of the captained charter. It is full time, so you won't be able to fish or scuba, but you would get a little snorkeling in. You usually have class at breakfast aboard, then have practical lessons all day and a written test at night. It isn't hard, but its intense and everyone I've known that has done it has become a reasonably good fair weather sailor in a week. Better, you will have an accredited certificate and know what you are doing.
If you can slurge, do the course over week one and then bareboat charter with just the two of you for week two. Other than the cost, the only downside I can see is that the two of you decide you don't like it. However, that would be the case with your captained charter as well.
Oh I agree completely. We will do this with a captain to get her feet wet on the open water. I've routinely fished 50-80 miles offshore but only power so I need to learn to sail and continue to learn the sea. If she thinks she like the sea then we'll take courses together.
I'm still in the acquiring knowledge about buying a boat but before I do I'll learn to be a newbie day sailor before purchasing it and certainly before captaining it anywhere particularly around docks and the public.
I'm looking to keep the boat at anchor in the Caribbean and SE US.