We're going (back) to France in the summer, but for the first time we're driving down and crossing the channel, rather than flying. We're going camping in Brittany, but I was horrified by the price of the ferry crossing that would land us geographically nearest, plus it's a 6 hour crossing and I get really sea sick. Any recommendations for the cheapest crossing for 2 grown-ups, a 5 year old and a car?