This fall we're visiting the Porsche Museum and Factory in Stuttgart/ Zuffenhaus. We're starting in Berlin, doing the Romantic Road, stopping in Munch and Vienna and ending up in Budapest. It's been really hard to find a rental car beyond the standard Hertz Passat - largely because of the out-of-country drop-off. I did try a specialized car rental place, which quoted $1,000+ per day (!) for a Panamera. Does anyone have a better suggestion, or should I just accept the Hertz buggy? It's such a shame to cruise the Autobahn in an "ordinary" automobile.

 

Budapest is a little problem, try to search for a car from Berlin, drop off at Vienna airport - which is on the freeway on the way to Budapest anyways.
You can easily get a S or CLS class MB, Jaguar XF, 5 series BMW etc. for a "normal" price if you drop it off at VIE. In Vienna, you can get a more regular car to drive to Budapest. Hertz know what they are doing not allowing you to drive to Budapest in an expensive car, trust me )) been there, done that, the trafiic is freaking crazy during rush hour.

Porsches and other exotic cars are a little hard and really expensive to rent in EU. most of the time you can pick them up and drop off only at the same spot.

 

would you consider stopping in leipzig after berlin? you can try to book a driving experience on the porsche factory track, and see the porsche factory and collection of classic porsches they have on display (assuming the factory isnt on summer vacation). leipzig is also interesting in its own right. picked up my cayenne at the factory there last week and it was an awesome experience!