The route we always use is Calais to Senlis (north of Paris) on the motorway, then the Francilienne (Paris outer ring road - NOT THE PERIPHERIQUE!!!)around to Evry, then the motorway again down to Nemours. The total toll cost for this, including caravan is about 30 euros. We then take the N road and on and off the various bits of motorway via Montargis, Nevers, Moulins, then Grannat, and on to the A75 in Clermont Ferrand. (Tolls around 9 euros). From Clermont Ferrand south this is a spectacular road - and you get to cross the new Millau viaduct (toll 7.70 euros). If you've three overnight stops I'd do Gien, on the Loire (just off the above route - and there's a municipal site right on the river - if you're lucky you'll see Osprey's fishing in the Loire), then around Clermont Ferrand somewhere, (volcanos) then down on the med south of Beziers somewhere. Three very different areas, plenty of sites (so outside peak season you shouldn't have a problem - and generally a much less expensive route in terms of tolls, than going down the Rhone Valley.