[size=12]There's a reference book specifically focusing on Griswold-made muffin pans, and appropriately enough, it's called Griswold Muffin Pans. It's copyright date is 1997, and it was written by Jon Haussler. It has a yellow cover, so if you hear people talking about the yellow book, that's the one. Even though the prices quoted in the yellow book are pretty high by today's standards, it's still a great photo reference for all of the varieties of muffin pan or gem pan, and it's often referenced when people say that they have a particular variation of a muffin pan.
Going on Haussler's terms, you have a No. 1 Gem Pan, variation 3. Haussler gives each variation a relative rarity rating, and of the three variations, this is the latest known and the rarest (6 out of 10 for rarity, vs 4 out of 10 and 5 out of 10 for variations 1 and 2, respectively.)
Haussler says $300-$325. I think Tommy's quote from the blue book is more accurate, but probably still on the high side. Though, given our recent debates about book values vs real world values elsewhere on this forum, maybe I'm just talking out of the wrong side of my body here. If I saw it in person and verified its condition to my satisfaction with my own two eyes and two hands, I'd have no trouble separating myself from $150 for it, and wouldn't sweat $180, neither. The fact that it's marked with a logo only helps you out here -- the other two variations aren't.
Just my opinion, I could be wrong.[/size]