I don't remember any one stone or precious metal being a great bargain in Aruba. They have Kay's and Shiva jewelers which I have found good gold and gem bargains. At Kay's (Same as in St. Martin) I had an Amesthyst set in a yellow gold slide and I get so many compliments on it when worn on a gold Omega necklace. Mexico ports such as Cozumel is great for Silver.
I just got back from Aruba for a 2 week trip there & hit every jewerely store there was. Here's the list of "what's hot".
Australian Opal - Basically a bluish/greenish color. Bought a ring ($160)& a matching bracelet ($315). Starting to come to the Caribbean islands, though it hasn't caught on yet. Stunning!!
Tanzanite - ALL OVER THE PLACE! Rule #1 when buying Tanzanite - the darker the stone, the more its worth. If you buy the lighter color stones, they are alot cheaper & to resell is just about impossible. Don't buy these stateside - overpriced. I would skip Tanzaite all together, the market is just flooded with this stone. I bought a good ring there anyway with 2cts and lots of diamonds - $415. Had it appraised when I got back home to see if it matched what the guy said it was appraised for. Yep, they matched in price! $1,900.
Black Sapphire - Another new stone currently hitting the market, stunning in color! But its not black, like another mix of greenish blue. But be prepared to spend some serious $$$ on this. Not many of the jewerely stores had this. Although that big jewerely store that's on the corner on the same street where the cruise ships dock had quite a few of them.
There's also all your other stones as well plus silver, gold, etc. Be prepared to wheel & deal. One thing I found out is if they buy jewerely from you, they take the stone out & melt down the gold or platnium and just place the stone in another setting to sell.