You can't have it both ways. If a town is nice/good/active (as Berlin is), the real estate costs will go up.
I come from Stockholm. where you've not been able to get a rental apartment for the last 25 years (not without getting into a queue for 15 years anyway) and a tiny studio apartment costs 150,000 Euro to buy. A whole generation has grown up moving around in second-hand apartments, and it's killing the city.
If you don't want to pay "high" rent, move to one of the many, many shithole towns that every country has load of; towns where nothing happens and that attract no "cool young people". It's what I did (although the smal ton I moved to turned out to be really nice, actually).
Good places attract people, and rents will go up - it's simple math.
Just be happy that prices are still as reasonable as they are in Berlin and that rentals are actually available at all. The situation in Berlin might have gone downhill, but it's still notably better than any comparable city anywhere else in the world. Easily.