Well i doubt whether anyone will buy it in ebay.co.in unless its of antique value. At the most it may sell for that value in ebay.com but i advise you to see whether any jeweller is willing to buy it for that price. The price of a necklace will be low when u sell it but since these are coins and that too minted in a reputed company it may fetch you the same price which u expect to get. I dont think that a gold coin looses it value unlike any other gold ornament. So try to sell it offline first and then ebay.com.