A few options to consider
Is it just your son going, or will he be bringing his family? What might work for your son alone might not for a family trip.
St. John, USVI might fit the bill in general, though. Most of the island is a National Park, so it is significantly less developed than other US Virgin Islands. Some of the most lovely beaches in the world, and pretty good snorkeling, too. You have to fly into St. Thomas, then ferry over to St. John. There are two timeshares on the island, Sunset Ridge Villas and the Westin, St. John. We have stayed at the former, and it was ok, but not luxurious and it has its drawbacks (water is not potable, for example - see reviews). The Westin is a high end resort and typically very difficult to get in to unless you own a Starwood property. As with most Caribbean islands, things are not cheap here.
St. Lucia at the Windjammer Landing resort, might be another option. Lots of information and reviews about this one. The island, while in-your-face poor, is beautiful, and the resort is lovely.
Your son might want to consider Mexico (Playa del Carmen area), where the beaches are gorgeous, the snorkeling is good, and costs are not nearly so high.
Another thought is Bermuda. In early Nov, the temps will probably still be good for the beach, and snorkeling can be quite good there. St. George's Club is the timeshare to shoot for. We loved our stay there and Bermuda in general.
Hope this helps,
Corinne
