Pets

Friends who have holiday homes here and have dogs usually come by ferry - Portsmouth to Bilbao or Santander; or Plymouth to Santander. These are operated by Brittany Ferries and take 21 - 32 hours depending on the route and boat. 

The dogs are kept in kennels on the boat and there is an exercise (toilet!) area. The crossings all involve a night onboard and I think some crossings do offer cabins that you can keep your dogs in with you (I'm not sure of this).

It's then a 600+ mile drive across Spain. Some friends do this in a day, while others break the journey with a stop at a dog-friendly hotel.

I think the ferry is about £500 and then you've got your fuel costs to get from your home in UK to the port, plus the drive through Spain.

The alternative is a 2-3 day drive through France & Spain, with 1-2 hotel stops and the tunnel. 

The costs are similar, depending on your vehicle's fuel economy and if you use toll roads.

Hope this helps!