We exported 2 cars to France.
Only because we could not sell them here.
The costs of transport were minimal, just drove them onto the ferry.
BUT the cost of registering them in France was significant over €1000 each for various bills such as changing headlights, NCT, road tax, new plates etc.
So in my experience what would have worked much better for us was..
Sell our cars in Ireland (v hard to do)
Buy new second hand car in UK..we could have upgraded by 3 yrs.
Bring UK cars to France.
We would not buy second hand in France because the prices are higher than Ireland.
Your main problem I think will be selling the Toureg
Good luck