What is the value of a 1939 deutsch mark coin?

It depends very much on the coin's condition and mint mark. A very good site for German coin prices is www.sammler.com However most of it is, not unsurprisingly, in German.

The page linked below gives values of 1939 1 DM coins. To translate, ss = well worn, vz = moderately worn, unz = uncirculated. Use a conversion factor of 1€ = $1.45.