Hi, What would be a reasonable price for this rare Johnson Matthey 1 oz gold 999 round bullion,made by the Selwyn gold mine operated between 1988-2003, I've been told this first gold bullions were made for the top notch officials and not many around.Written 'Johnson Matthey' on one side and 'Selwyn First Gold 22.4.88 on the other' .Comes in the blue original Johnson Matthey plastic sleeve.Thanks very much in advance.