Hi david,
Taking a plane would obviously be the fastest way to get to France, but if you're looking for something at a lower cost, then a Ferry or train would be the way to go. It all depends on how much you want to spend to get there and how fast you want to get there.
I couldn't find an exact price for a ferry since I didn't have your car's make and model, but here is some info for you to look at:
Ferries
Also, if you want to fly, what city in France would you fly into? (I am unable to find Brittany France).
If you need anything else, please feel free to ask.
Also, please remember to click ACCEPT and take a moment to leave me POSITIVE feedback