Mileage points from credit cards are definitely a great way to get cheap plane tickets. I am currently in Japan and I only spent $56 USD for round trip flight from Detroit to Haneda Airport thanks to miles. Now that I think of it, I don't think I paid full price for a plane ticket to Japan in the past few years. Not sure if you can do this in Germany but I just churn credit cards for the miles. Check out /r/churning on Reddit if you want to learn about how to do this.