Background: the German registry, DENIC [denic.de], is not a for-profit corporation but a cooperative owned by its members [denic.de]. The members are web hosting companies; they get domain registration cheap, typically package it with hosting and resell that package. There is a direct registration service by DENIC for the public but it's prohibitively priced (intentionally, it seems).
Price example: In the hosting package that I use personally, an additional .de domain is EUR 11.88/year. There are hosters with still lower prices