Nothing. Absolutely nothing.
EDIT: I have asked an older student and before the 1970s there was in fact
a so-called "Hörergeld" "listener money" which was in the range of 100-200 Mark (comparable to 30-45 $) for half a year.
The interesting thing is that is was not for the university, but for
the professor, so while there was charging, the answer is still correct.
I myself paid 120 Mark for half a year, but this gave me the right for
unlimited public transport in the area, so I did not count that.
The Hörergeld during the 1900s should have a comparable range (neglible
for wealthy students, perceptible to students working part time), because
Albert Einstein lamented that there was opposition to allow very poor
students listening to the courses.
This may come as a complete shock to people especially from the US
but the concept of Universities charging their students was/is completely
foreign in Germany. The running costs are paid by taxes from the government.
There was always the firm belief in Germany that people have a right of
education. This was so ingrained that students
- had severe discounts on lodging, visiting libraries, cinema and public
- lived together with many people in bigger apartments to share the rental
or living in subsidized lodgings, "Studentenwohnungen".
- had after the 1970s a right to get financial support from the government,
the so called "Bafög"
- there were no limits how long your study take. You could choose to do
it in minimum time or 30 years long.
- you were not obliged to attend a lecture. You could completely disregard
the lectures and study yourself, the only thing you needed was to pass
the tests. So many people were able to do jobs part time and were able
to finance their education.
In fact, I am one of the German students who did his "Diplom" with exactly
this conditions. Now you may think that it may have changed, but
you need only to read Mark Twains "A Tramp abroad" in the 1880s to see that
it was the same in old times.
During the Bologna process starting nearly exactly with the beginning of
the 21. century the old process was "reformed", changing Dipl. to Bachelor
and Master and introducing charges as "Studiengebühren".
But due to problems with the organization and general disappointment with the
system, "Studiengebühren" were mostly scrapped again.