I think that seeing how your car is not owned outright(leased car or even one with a lien), this will be a deal breaker for your ED trip.
Plus realistic shipping rated will be about $1,500 each way. That is with all the broker fee's and duty. Plus your gonna need insurance while your over here. You won't need German plates(you can drive with US tags for up to six months I believe. But you WILL have tp post a bond, so that your car leaves Germany after a certain amount of time. I think after six months. You can also opt for one year... but the bond amount you have to put up is huge. I think realistically you are looking at $3K for shipping (round trip) plus $1K for fee's plus bond (probably another $1K in cash).
You'd be better of just to do an ED on a new car and then sell it once the car arrives back in the states.
Check with www.Sixt.de
for good rental rates. They rent everything from Opels to Ferrari's. Make sure you tell them you want to rent the car for a month - that way you will get their lowest rates. You will also need to be over 25 years old.