Investing, Stocks, Mutual Funds

I have heard my mother talking about the fact that her father used to have a Saint Gaudens Gold Coin, and wondering what ever happened to it. I am trying to find out whether or not it is easy to find these coins for sale since I was thinking of getting one for her since she really seems to have liked this coin. Are Saint Gaudens Gold Coins very valuable? I am hoping that they will be within my price range so that I can make her smile by giving her one for her upcoming birthday. Can anyone tell me where I can find out more about these?