Think I'll hang onto this. I've been collecting for quite a while, and haven't seen one of these. Even on ebay. Normally on ebay, there's something of everything listed, even if it's at obscene prices.
Was talking to one of the guys at the below site today, basically said value is really hard to establish unless sold through auction. He SWAG that it is likely to be $100+ given rarity, ease of identification as an error, and collector interest in engelhards in general.
Yeah, it just sold.... I'm probably going to list mine up and see if I have any takers. If it sells, it sells, if not, it doesn't. If people have stupid money to spend on these things, 75X spot price or trading 1 ounce of silver for .9 ounces of gold, that's fine with me.