Have a look on autoroutes.fr ,if you put in your ferry terminal to your destination it will tell you the road toll cost and a rough idea of fuel, obviously the fuel depends on how good your van is too the gallon but it will give you an ideaT:
Annecy is stunning!, if you haven't been there you are in for a treat T:.
I have no idea what it cost's to drive there, I flew to Switzerland and then got a bus to the French alps to my Uncle/Aunt's house, we ended up driving to Annecy from there. The whole surrounding area is lovely. Lot's and lot's of lakes and mountains.