Some of us learned to drive the Autobahn by practicing on the 'good' portion of the A8 in a 2CV (And earned their only speeding ticket ever on a country road in said vehicle, but that is another thread)

OP, Hertz sometimes yields some very good rates but you do need to fiddle around a bit between the .de and the .com sites, and log in or don't log in. If you have the time and/or the patience you can often find some very good prices on an automatic. Expedia.de also yields decent rates sometimes, but there is a cancellation fee involved there. A small car with Hertz is often a Mercedes A class, or an Opel, sometimes a Ford, or very rarely a VW Golf or Polo. In my experience the A class has less power and less fuel economy than one of the VW options, and I recommend asking for diesel.

Sixt also offers a lot of discount programs; their 'Ladies Program' seems to give quite good rates, for instance.

Re the 'thrill of the Autobahn' I find that the biggest difference with driving in America is the left lane rule. Drives me crazy to have people not move to the right in the American states where that is permitted. And I like not having to 'shoulder check' on the Autobahn.