[size=12]I'm looking in the Yellow Book (Jon Haussler's Griswold Muffin Pans, which is a guide specific to bread pans, muffin pans, and the like. The actual book was published in 1997, so adjust mentally as you see fit.
Haussler gives each pan a price range and a rarity rating. He says that your pan is very rare (9 out of 10, where 10 is the highest,) but that it's a "mysterious" pan about which little is known. Griswold made a No. 21 bread stick pan (p/n 961) that was identical to this pan but had their name cast onto it on the bottom of section 2, and EPU cast onto the bottom of section 5.. (Those have a rarity rating of 5 out of 10, by the way...) The mystery seems to be centered on why they made one that hasn't got their name on it. Haussler's picture also has hang holes drilled in each tab, just like yours, so you can rest assured that they were probably both factory original rather than drilled after the fact, in case you were wondering. It might be that this was made for hardware stores to sell as their own stock, like a lot of the other unmarked pieces, but that's just a guess.
Haussler says $800-$1000 in 1997. He amends this by saying that a lot of collectors aren't too keen on this pan, since it's sans Griswold markings. Still, though, it sounds like it's a rare bird. I'd hang onto it, were I you.
I'm no expert on muffin pans, by the way. I have a few, but it's not a focus.[/size]
