any suggestions for a car service to drive us from Frankfurt airport to Sasbach Germany?

try https://www.blacklane.com/en

That is about 120 miles so I'd guess a car service would cost a fortune - you could take a train to Baden Baden and then Achern (or even a cab from Baden Baden)

If your destination is Sasbach near Achern you could go by train to Baden-Baden as suggested above. From BB there are buses to Sasbach. If your destination is Sasbach am Kaiserstuhl you could go by train to either Offenburg or Freiburg, transfer to a train to Riegel and there to a bus or train to Sasbach. If you prefere going from Freiburg to Sasbach by taxi, the Freiburg taxi cooperative gives a quote of €86.30 for the trip.

Addendum: The Sixt limousine service at Franfkurt Airport gives a quota of €564 for the entire trip with an Mercedes B (cheapest class).

Thanks to you both!