The Finals of the Eurovison Song Contes is on 05/14.
and iīm afraid the whole area will be fully booked for the Weekend. Itīs an international Event and some 30.000 Vistors are expected for the Show ( at least the organizers hope so).
Maybe you are lucky in Essen, Bochum or Dortmund (all relativly close to DUS)., but donīt expect to find a 5* Hotel there, there arenīt any afaik.