...or VHS, as it's called on the street (and no, it's not another name for one of Berlin's drugs)…read more VHS is the community college equivalent system for Germany. They offer much more than just German language courses... they have web design, tap dancing, yoga, French... you get the idea.
The registration process can be a little overwhelming, signs are all in German with conflicting information from the internet... but if you are persistent, you will get into a class. I just finished my first course of German A1.1 (first level) and I am 100% content and satisfied. Price is 150 (cheapest school available in Berlin). They do not check visa/work/student papers- anyone can enroll! And they DO accept cash. You do not need a German Bank account like their website states.
My class has mostly older adults who are serious about learning. Thus far, I've only had two teachers (they take turns teaching the same class) and both are excellent.
If you are looking for a 100 in-class hours (about a month long) German language class or many other languages at a great price, I highly recommend you enroll at your local VHS. They have at least one location in every district of Berlin.
To register you will only need your passport, Anmeldung (legal registration of your address), and 150 euros!