On the other hand, it is hard to believe you can rent a
    200k€ place for 500€/m. In Warsaw, a 2-room 40-50 m² 
    apartment in the city center costs about 400-500€/m to
    rent, but if you wanted to buy it, offer prices start
    below 100k€.

Believe it! Or look at http://www.immobilienscout24.de/ for Berlin (in the combo box right of the search field "kaufen" means buy and "mieten" means rent - pick the first option in both).

There are places that are unusual (like Mitte - the center of the city), but for ~90%+ of Berlin the pattern I described above more or less holds.