From near Exeter our obvious choice is to get there via Plymouth Brittany Ferries. Now you may think this is a silly suggestion for you nearer Calais. Cost-wise it may not make sence. There has never been any problem with ramps on or off Brittany Ferries. The West coast route down through France is less busy and avoids Lyon. (I hit a chunk of wood that had fallen from a truck and damaged the undertray of my VW Passat down that way!).
If your heading for the South West of France I would give it some thought but if your heading for the South East then I suggest the scenic way down Route Napoleon if you are not in too much hurry. Newhaven / Dieppe ferry might avoid congestion at Calais - It is was one of the no frills cheap and cheerful operaters.
