This is something we have talked about a few times here. I saw a new website today that tracks not only the PM prices, but watches eBay around the world and tracks what these coins are going for and what the premium over "spot" is.
http://www.24hgold.com/english/buy_sell_gold_coins.aspx?co_id=0
http://www.24hgold.com/english/buy_sell_silver_coins.aspx?co_id=0
Fascinating, these coins are averaging 30-40% over spot, and up over 100% in some cases.