@JO: Lucky you, recently spent 4 weeks around in Germany, typical landing fees are i.e. between 12€ and 18€ for a <1.2to and a usual mid-size GA field, very few cheaper - didn't encounter any less 8€, lots more expensive - everything up to 35€ for <1.2to is thought normal (some strange lateron bills from german DFS included).
First things first, I usually pay between €7 - 12 for a P28A so don't know who charged you so much. Secondly, had I known you were intent on flying around Germany, then I would have recommended you buy the Landegutscheinheft from Airshampoo - there are two books dividing Germany into north and south, each offering free landings at 40 airfields per book.
With the book, you can then land up to 3 times at selected airfields without charge. Oh, and they're not just smaller airfields either.. Want the experience of an international airport - land at Paderborn or Hannover. Want to experience the North Sea Islands? Land on Wangerooge.... I could go on but suffice to say the books are well worth it, saves me around €140 a year in landing fees per book.......