You can find those prices on older Queen Games in all Kaufhof shops throughout Germany. Not every shop carries all of the games but those are the standard Queen Games prices at Kaufhof. If you are lucky you can even find Thebes and Batavia for 10€ each and Airships and Fangfrisch for 8€.
Very close to Hamburg airport is www.magierspiele.de You can reach them by bus from the airport. I did this once myself. They are one one the cheapest boardgameshops in germany. They carry Strasbourg for 30,10€