Yeah, seems a little out of place here.
There are several better choices:
Professional but awkward: Musikschulen (music schools) are maybe the best bet, though they are always private schools ( = higher tuition fees) and normally specialized in teaching children and young adults. It can be quite a mess to find one offering adult classes. Often offer solo-courses. If they want more than 50,- per unit (45 minutes) you're about to get robbed legally.
If you're feeling lucky: Volkshochschulen (a bit like a community college, but without academic aspirations) often offer music classes. Problem: Most teachers are not certified teachers, but professionals in their respective topics. So it may happen, that you find an interesting course, with a highly qualified musician as a teacher, who is less than qualified to teach.
Prices are mostly per course, not per lesson, so don't be bothered if their offers are in the several hundreds-range, but always calculate the price per lesson, to get a better idea of regular tuition fees.
Best bet for cheap courses is to go to a conservatory (like the aforementioned Robert Schumann Institute) and put a note on the noticeboards there, enquiering what you're looking for and offering 30,- per lesson as your bid. No need to write it in German, most students there should speak English quite well.
Good luck!