Hi
I have just returned from taking my furniture over to Condado. I also took the ferry to France then drove down the east side of France: Calais-Lille-Toulouse to Barcelona-Valencia-Alicante-Murcia. I took the AP7 from Barcelona to Murcia which is pretty much a straight run but is a toll road. My advice as follows :
1) If possible, mr recommendation would be to take the ferry from Portsmouth or Plymouth to Bilbao (or Santander). It costs approx 250 euros (without a cabin) and means 24 hours on the ferry followed by approx 12 hour drive past Madrid to CDA. The time on the ferry will leave you refreshed enough to complete the drive in one go (with breaks). Also the cost of the ferry will work out cheaper than paying for fuel / tolls driving through France.
2) If you decide to drive all the way and take the route you mentioned it will cost approx 100 euros in tolls for France & the same again for Spain as well as fuel - approx 200-240 euros for the whole journey. Be prepared for a long drive as we had 2 drivers but still had to stop one night in the van - there are plenty of truck stops at service stations with showers/petrol/cafeterias. The whole journey took approx 30 hours (excluding breaks) from Birmingham.
3) From Boulogne - if you want to save on tolls / time then ideally you should head to / go around Paris - then south to Cartres - Tours - Poitiers - Bordeaux - San Sebastian - Pamplona - Madrid - Murcia. This is the route I took on the way back but would follow if repeating the journey.
4) Avoid Andorra as I found out to my cost. They're not part of the EU so if you try to pass through Andorra you will have to pay tax on everything in your van. I had to turn back & drive around the Pyrenees which added hours to my journey.
Basically, it's a slog but a great experience albeit an exhausting one. Make sure you take a camera as the scenery is magnificent !
Good Luck !!
San