21 year old boy, looking for accommodation in Darmstadt

I am Erasmus student. I will come to Darmstadt in 28.09.2016. However i could not find a dormitory or another place to sleep. The private dormitories have at least 550 euro rent. It is too expensive for me. I can handle with at most 350 euro rent. I am not smoking, not noisy person, and i am well adjusted person. It is not important to me that a roommate, flatmate, dormitory, room, apartmant, noise etc. I just want place to sleep.