Hi Debbie - you didn't mention if the ring is mizpah antique jewellery or not. There is a legend that has evolved around Mizpah. Not all mizpah jewelry is old, you can buy fine, new mizpah jewelry today.
Debbie, you mention the ring is large, which is consistent with tradition, mizpah finger rings, were in the form of a wide gold band engraved or embossed with the word "Mizpah".
The value of the mizpah ring will also depend on other factors such as the weight and gold cartage against the current price of gold. Gold prices hit records today.
The meaning of Mizpah literally means "watchtower" but in modern use, it is a parting Hebrew salutation. It was a good luck talisman and traditionally given as a gift to a parting soldier.