Answer:
You should have your coin evaluated by an expert in European issues. According to sammler.com, a major German collectibles site, it could be moderately rare. Values as of 03/2012 are
Moderately worn: €220
Slightly worn: €420
Uncirculated €650
Only 29,000 were struck. They were issued by the state of Hesse-Darmstadt which was semi-independent at the time.