Thanks for the input, everyone. He's not a numismatist, so I've stressed to him how to properly handle coins since these pics were taken.
I know the area where he supposedly found it, and it is definitely an old Spanish fort in NOLA. Ostensibly he had permission to detect there. I'm prefixing these statements, as I have not known him for a long time. But based on the other artifacts he's found - hatchets, cannonballs, uniform buttons, etc. I have little reason to disbelieve him.
Unfortunately, the attribution is by word of mouth, and anyone can do the same with a coin.
He is thinking $175 - is that unreasonable?
Inordinately fascinated by bits of metal with strange markings and figures