I have no idea what the prices are in St Thomas for cameras. but in general here is my take.
You would be better off buying from Amazon (or another online retailer). Typically duty free doest account for that much, and it is always off the retail price. In fact, many of the duty free shops (electronic, jewelry, etc) are partially owned by the cruise lines (or get kick backs), that is why there is such a push on you shopping at specific places.
Here are a few reasons I would NEVER buy a camera (or similar type product at a port):
When I buy something new, the expectation is it is in a sealed box. If the box is opened (becouse of a return or a store display) it is no longer new and should be sold as such. Most stores like this use the new inventory as display. Who knows who has touched or messed with it, or what has happened to that camera since it came out of the box.
Caveat Emptor!
You may find that the camera you are buying doesn't have the same (if any) warranty, as they could be gray market cameras. Should you have any problem with the camera, or want to exchange it, that option doesn't exist.
Another issue you get into with buying any DSLR, is you aren't just buying a camera, you are buying an ecosystem. The real cost isn't the body, but the lenses. Obviously for many people they only use the kit lens that comes with the camera, If this is the case you are better off with a DSLR-sytle camera that has a built in lens. It is non-swappable, but will often be a huge zoom range. For example this
sony camera has a 24-600mm built in lens. Although if she does want to use different lenses (maybe she already has some lenses?), they your buying choices become much more focused (no pun intended). Which may even make it harder to find a deal.
Lastly, since this is a big purchase, both financially and considering the ecosystem of the camera, you should do some homework as far as specifically which model you want to buy for her. There are many things to consider, brand, price, body size, capabilities, reliability, performance. After narrowing that all down, you may realize that finding someone that sells exactly what you are looking for may not only be hard, but also may not have much or any discount as it is too popular of a camera. Especially if it is a recently released model. My guess is that the cameras with the greatest discount are ones that companies are trying to unload.
I think a nice DSL is an incredibly generous gift. I just wouldn't buy from an unknown source just to save the perceived couple of bucks. Not to mention spending hours of precious time on vacation doing something that could be done online in 15 minutes.
Well, that is just my 2¢, other people my feel different.
