I rent half of my 130 sqm appartment which contains one spacious bright room + private bath + own balcony + shared kitchen + living room in the fancy neighbourhood of Neukölln, close to the metro and two parcs (Tempelhof airport). For 1 person 25 €.
Please do not smoke inside - the appartment has 2 balconys..
Nice, clean house with students, families and friendly people. My neighbourhood used to be turkish/arab dominated and is now flooded by students, artists, tourists,...but it is still okay ; )
Metro 3 minutes to walk - takes you to Alexanderplatz in 12 minutes.