These are extremely interesting pieces. Not only are they interesting collectible coins, but they have some amazing stories attached to them. Strict coin collectors do not like them because they are very commercialized, but the rest of us enjoy most everything associated with sunken treasure. And that is just what these coins are!
Approximate values are given on our page about Spanish Colonial Cob Coins. This page has background material for cob coins that are also treasure coins.
The Atocha was a Spanish sailing ship that sunk off the Florida coast laden with gold and silver coins from the New World. The 200+ people onboard never made it to Spain, and neither did the coins. Mel Fisher, a famous modern treasure hunter, salvaged over 160,000 coins from the shipwreck site. A tidy business has been built around these treasures. The El Cazador has a similar story with a slick web site at this link (click here).
Please check our appraisal for Spanish Colonial Cob Coins. Here you will find pictures, sizes, and a list of nominal catalog values.
In general, normal retail mark-up factors apply to these coins. If the coins sells for $X retail, it sells for one-half of $X wholesale. So, if you find one on sale for $500, a dealer would probably pay you about $250 to buy it from you.
CoinQuest thanks Atocha Treasure Coins for use of their silver coin picture. Be sure to visit this site and others like it if you are interested in these neat items.
With sunken gold coins all the same factors apply, only amplified. The gold coin in the picture comes from the Vliegenthart (Flying Hart), a Dutch East Indiaman (trade ship) and it has been artistically mounted in jewelry. The coin itself is an old Netherlands Holland ducat, which contains 0.111 troy ounces of gold. If gold were, say $1000 per troy once, that would be $111 worth of gold (look up the current values at kitco.com). But the coin itself is worth more because (1) it has coin collector appeal, and (2) it has treasure hunter appeal.
Again, it is up to you to assign values to the 'appeal' factors.
Our gold picture comes from LostGalleon.com where you can find all sorts of related items on sale, and CoinQuest thanks them for use of their coin photo. It is a beauty!
Another page on treasure coins, this one with a large silver 8 reales, appears at this link [Click Here].