unless it was an offer direct from the mint, chances are you guys got gyped. i've heard of special promotional offers but nothing as insane as $10 for a $50 face value coin (typically prices are face value + some)
when i say plated i mean it has a very thin layer over another type of metal. copper pennies are like this now (plated not solid). the layer can be very thin (like a few pieces of paper thick) or less. its not sprayed on..
http://www.google.com/url?q=http://www.ehow.com/how_4601441_gold-plate-metals.html&sa=U&ei=yLGyTt7eAdC_tgehkvnbAw&ved=0CB4QFjAC&usg=AFQjCNE78qPaC3Vx0bDMq958Eza_vKJJqg
knowing how you got the coin, it might or might not be real gold. if it is, it most certainly isn't solid.
all legal tender in the usa MUST have the face value printed on it. i've never heard of one saying copy either. most likely its a knock off product.