It sounds like you have one of those novelty items made by enhancing an uncirculated American Silver Eagle (ASE) bullion coin. Currently these items sell as novelty pieces for $50 or $60 US dollars. A normal ASE contains one troy ounce of pure silver and these sell at about the current price of silver. Use a web site like kitco.com to look up the current silver price.
For an untreated coin, the value is figured by starting with the spot value of pure silver (about $13 US dollars per troy ounce when this appraisal was written) then adding premiums for the fact that the precious metal has been struck into a coin and backed by the US government. Then add dealer's margin and you quickly get to the $20 to $25 mark. The value of silver changes every day, so be sure to look it up.
A treated coin has been defaced, so it is worth essentially nothing to coin collectors. Painting a coin is one of the most severe methods of damaging it in the eyes of numismatists (coin collectors). If you try to sell your coin to a collector, he or she will not buy it for more than the raw silver content. If you put it one eBay, a non-collector may buy it for the $50 or $60 price. If you try to sell it to the owner of a novelty shop, he or she will probably pay one half of the retail value, or less.
You can see examples of enameled coins from Great Britain at this CoinQuest link.