How much is a deutsche 5 mark coin worth now?

It depends on its date and design. Standard 5 DM coins dated 1975 through 1996 and with the number 5 inside a squared-off oval are only worth a premium in uncirculated condition. They were in common circulation until Germany switched to the euro in 2002; at that time they had an exchange value of about US $2.50

If your coin has a different date, different design, or is made of silver it could be worth more. In that case please post a new question with more details.