How much would genuine 17th- or 18th-century Spanish pieces-of-eight be worth? Would it be based strictly on it’s silver content, or would it have additional value as a historical artifact?
Like any coin, they are subject to their rarity and condition. Here is one for $375 dollars that looks to be in good condition.. There are websites that specialize in vast quantities of old coins. History doesn’t usually play nearly as big a part in value as the rarity does. You can have large quantities of 2000 year old Roman coins delivered for relatively little money because there were so many produced and still around.
Depends on what kind of shape it’s in and it’s provenance.
If you have something in good shape from a known wreck, it will go for more than a non-descript, worn hunk of silver.
Well, the Washington Mint wants $149 for them; considering that silver is now at around $12.50 per (troy) ounce, and the things are described as weighing about 0.9 ounce, most of the value derives from their historical interest. 
JRB
If you truly want the irregularly shaped 8 real coins from the pre-1732 period, then you are looking at something over $100 and way up, depending on condition(whether it is a sea-salvage piece or a “land” piece is important). While something with the glamour of a “Atocha” coin brings $1000 to the tourist trade in Florida and the islands, I can buy you a genuine “Atocha” 8 real, depending on the condition, for $150-300. Same coin.
If you want the later “bust” 8 reals which started in 1772, then I sell these to the public for about $55. I can wholesale all of these I can get for about $45 each, and then they wind up as items that sell for over $100 each from companies which promote coins.
The 8 real “pillar dollars” which are the round ones produced from 1732-1772 are bringing about $150-225 currently, depending on where you get it.
I own a Piece of Eight that was salvaged from the Spanish Galleon–“San Jose”. This ship sank during a hurricaein July, 1733. Could you please tell me the value. Thank You–Jim Nowicki
About 5 braiiinnnsss
Go find a reputable coin dealer in your area and ask them. We can’t do something like that over the web.
I’ll give you five bucks for it.
Regards,
Shodan