Hi Jeroen
The Madrid area, specially the Barajas surroundings are a bit expensive, due to the nearly of the airport.
Barajas is full crowed of airlines workers. In my opinion, you should try to find the flats announces in your company show room office.
Also, take a look at
www.segundamano.es , and there, go to the renting flats.
Hope it helps
Regards from Spain