FYI some figures from the 2014 trip.
Bristol to Riva with 1 bike, 2 boats, 4 tents and 4 people return cost £853.64 (fuel and tolls).
Including accommodation (campsite) and ferries this worked out at £350 a head for a week.
Sailing 2 boats from Riva cost £80 for the week's launching fees
Driving time was 24 hrs door to door each way.
That is travelling the "expensive" way through France. The the total cost for the car and tolls, including £141 to insure 2 young drivers. However, it does exclude the world's best Burger King (somewhere in France).
**Note first post missed the ferry and camping cost ***