Berlin only has high rents compared to Berlin a view years ago and some, uhm, small places ;)[1]. Compared to many European capital cities or at last other large cities in Germany Berlin rents are still quite ordinary or even cheap (through the 600-900€, for a 55-60m² are right in Madrid for example that would be more like 900-1500 and in Munich its 1500+).

[1] not sure how to express this, I mean just because it's a "small" place it's nor any worse just a bit different.