Hi Martin,
I don't have experience with importing to Germany, but I do live in the neighbour country Netherlands where some of the same rules apply (because European Union).
Probably there are at least 2 taxes to take into account:
-#1: european sales tax: no sales tax was paid over this car and you will still have to do so. This will be calculated based on the current value in germany of the car * 19%. If you want to get an idea of the value of your car, check
www.mobile.de and search for a comparable model. Say this is €25.000 * 0,19 sales tax *1,2 to convert to dollar = $5,7k
-#2. vehicle tax (based on for example emission, engine capacity, etc). This is country specific and the newer the vehicle the more expensive the tax.
It wouldnt surpise me that all-in (incl shipping the car, taxes, registration, etc) you might have to spend close to 10k USD.