That's a Navy administrative officer breast pin, like you can find here. They're not particularly uncommon. A rudimentary search suggests they go for about $100 in collectors markets. I should note, that yours appears to have been damaged, as there should be a hook coming up from the bottom (on the back) that stabilizes the pin when it's being worn.

This looks like a pin from the Kyffhäuserbund, an umbrella organization for War Veterans and Reservists Associations in Nazi Germany. I could be wrong though.