Cheap accommodation relieves the strain on your student budget enormously. The rent, on average about 250 Euro per month, is the largest monthly expense for students. However, the amount of rent depends mainly on the type of accommodation and the place of study; especially in the New Länder (East Germany) the average rents are lower and a room in student accommodation is also cheaper than a room or a flat on the independent housing market.
In urban areas and the classic university towns there is very little cheap accommodation. Especially at the beginning of term it is often difficult to find cheap rooms and flats. Begin as soon as you can with your flat search!
Students on an exchange programme often have it easier than the students who organise their studies in Germany themselves. This is because they are usually provided a room in student accommodation. Enquire at your university in Germany!