Here's the route we use:
N43 (Green sign - signposted Paris) from Calais towards St Omer, Douai, then Lens, then N 17 down to Compeigne, Senlis, then across to Ermenonville on the yellow road, back towards Paris on the N2 for a couple of junctions, then take the E104 (or A104) around Paris, following Marne La Vallee signs, then keep on the E104 until you reach junction 32. Take the A6 a couple of junctions (toll only a couple of Euros) until you reach junction 15. Then take the N7 down to Cosne sur Loire, where it becomes N7 auto route. Might be a couple of very small tolls, then the N7 agaom dpwm to Nevers, Moulins, then head on the N9 towards St Pourcain sur Sioule, Grannat then the auto route to Clermont Ferrand (couple of euros again) and down the A75 to Beziers.
From Beziers continue on the N9, around Narbonne, then take the D6009 along the coast until it turns into the D900, follow this through Perpignan (not at all difficult, very well signposted) through to Le Boulou, and so on down into Spain. Keep on the non-toll road in Spain (haven't a map covering this handy) and you'll see the signposts, not that far, for Rosas/Emporias.
Have a great trip. Get a good map book (Michelin is good) and a sheet map for northern and southern France (Recto-Verso - from Michelin). Highlight the route in pink on the sheet map, and use this for main town to town navigation, and then the detailed Michelin for the bits around the towns.
It sounds much more complicated than it is! Basically remember that Motorways are always signposted in blue, and if you have to pay it will have 'Peage' at the side. Non-toll N roads are signposted in green (sometimes both options appear on the same sign holder - follow the green signs).