My mom has three for sale right now at her antique shop. The prices are between $300 - $600. And they don't last long. Most that I have seen on eBay go in about the $200-$400 range. But I have seen them go for closer to $800. If you do an advanced search you can choose for it to pull completed auctions too. That will give you a feel for what the current 'rate' is.
But Bobbie is right - set a price in your head and stick with it. You might lose it, but there will always be more. They can be hard to find but are definitely not 'rare' or one of a kind. HTH