Hi Steve,
I had the same thought as you last year, toll roads pricey, so we'll go on toll free roads. Never again!! Like you, we went through the tunnel, travelling to Le Pin Parasol in the Vendee. I planned 2 routes, using Via Michelin, using the toll roads, and toll free roads.
Although the toll free route is scenic, it's very time consuming as you keep going into villages with speed limits. After about 4 or 5 hours I got fed up, and went to plan B and joined the toll roads for the rest of the journey. Our total journey time was about 10 hours, including a brief 30 min stop. We had our 2 kids, 11 and 8 yrs with us, and it was a long drag for them.
This year we're going the same route, but using the toll roads. I think (but i'm not sure without checking) It is cheaper to go via Rouen, Caen, Rennes and Nantes, as there are more toll free motorways, instead of going via Le Mans. It is slightly longer distance wise, but this is the route I've used in the past when coming off the Ferry at Le Havre.
Thanks,
Lara