I can't speak for the whole league, but at Hertha ticket prices run from about 15 euros to 75 euros, depending on who they're playing and which part of the ground you want, with 15 euros being the cheapest ticket against FC Nurnberg, and 75 euros being the most expensive ticket against Bayern Munich.
I was just over in Celle/Hannover and the guy there said it was from about 12 Euros for a Hannover game. But then they have not won in a while...