https://uk.cars.yahoo.com/news/germany-charge-foreigners-autobahn-131328458.html
I guess 10 euros isn't a big deal for a 10 day disc, it'll be a pain having to order one before you go though.
Including where to go to find the faster stretches and some of the debate about derestricted highways (with a US slant)
http://www.bloomberg.com/news/2013-08-18/go-east-370-hp-bmws-find-thrills-on-fast-german-autobahn.html