I believe what you have there is a commemorative medal that was produced/distributed by the National Historic Mint (NHM) of New Jersey back in the 1980s. They sold a variety of "Double Eagle" commemorative medals at the time, including a US Presidents series. Some were sold in sets, some individually. I've seen medals for Ronald Reagan, George Washington, Thomas Jefferson, John F. Kennedy and Franklin D. Roosevelt. I'm not sure whether they produced a medal for all of the presidents, however.
Based on what I've seen of the NHM medals -- and the appearance of yours -- I would venture to say that the composition of your medal is a base metal (either copper or nickel) plated with a thin layer of 0.999 fine silver; this was their standard. Some of the medals sold by the National Historic Mint also had selective gold-plating on them.
Its current market value would be no more than $10.00 -- the amount of silver in the plating is negligible and therefore doesn't really contribute to the medal's value in any appreciable way.
Hope that helps!
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