Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Columbus to Dortmund as you normally would.
Dortmund (DTM) is the airport you will fly into if you book a flight from Columbus to Dortmund. You should not have trouble finding flights to Dortmund from Columbus; the airport handles an average of 0 inbound flights from Columbus per day. You should also have plenty of airline options to choose from since 0 airlines have flights to the Dortmund airport from Columbus. It is only a 6.3 mi journey from Dortmund (DTM) to Dortmund’s city center.