I drive often, from Saxony, Germany to South of France, Bordeaux region. In the past there was an option to put your car in a train and drive to Paris and from there, drive further, either by train or by yourself. However now I wasn't able to find it anymore.
For example, for Strasbourg to Bordeaux, prices currently are:
- 85 Eur (some kind of car rental system, depends on driver availability)
- 419 Eur (truck, 9 days)
- 820 Eur (professional driver, 3 days).
On the German side, there are only a few remaining trains in N-S/NW-SE direction. Autoreisezug-Planer has a map (red/orange stations are in use, white ones are closed), and more details in German (menu on the right).
According to the helpful map on the Seat 61 website https://www.seat61.com/Motorail.htm there are southbound motorail services still from Paris including one to Bordeaux and also services southbound from Düsseldorf but those only go to Italy or Austria so you are out of luck.