Two Dominican's I know....
................have two of the metal detectors that are submersable and are of good quality ($500 to $600.US) that were brought from the US by their family. They have been using them on the beaches in Cofresi and Costambar and I know that they are at the Compra Venta every day (not quite but you get the point) selling stuff.
They have found QUITE a bit. We have one that is not that good quality and find much much less. My watchman and gardner use it every once in a while and find more "peso's" than jewelry.........I think you need a good machine to find the good stuff.....