I decided to only get the full ferry one way - I'd ridden down to near St Nazaire to meet up with family, then got the St Nazaire to Gijon (Hee-Hon) ferry. Overnight, two people, two bikes, en-suite cabin - £120. We couldn't have ridden to Galicia from St Nazaire for that much in fuel alone, so the night's accommodation was free!
I'm a big fan of overnight ferries - in a hotel you stop travelling when you sleep, with ferries the journey continues - so for the less interesting bits it's free miles.
I would suggest if you want to do ride down+ ferry back or ferry down + ride back you choose the first option. Riding back to the UK from the Pyrenees is quite a trip, if it's at the end of the holiday it can feel like you're holiday is already over and you've got two days of travelling to get through. If you ride down then it's all part of the holiday, by the time you get on the ferry for the trip back it still feels like part of the holiday. Next thing you're at Portsmouth and nearly home - it feels great.
We got a bit carried away with the ferry on the way back and ended up with a Commodore class room. Needless to say at the "Club Class Check-in" we were the only two people wearing leathers! The lass very politely asked if we were lost and looking for the main reception
Fair play to her though, after we showed our tickets she was great and kept bringing us freebies to the room
If you go to Andorra try and be there mid-week rather than weekend - the place gets absolutely rammed at the weekends. Andorra la Vella is full of bike shops selling some very cheap gear (crazy low tax in Andorra) so it's worth staying two nights and having a day off the bike wandering around. Caldea (cal-day-a) is a big swimming pool spa thing in ALV, great to go get a massage and some serious relaxation after a week on the bike.
We stayed at a variety of hotels and B&Bs, our route along the Pyrenees followed closely to the Franco-Spanish border. The roads do seem to very depending on which side of the border you are, the French passes tend to be more technical while the Spanish side seems to have more of the faster sweepers. Both are great. I rode a few of the great Tour de France routes and climbs (Tourmalet, Aspin, Peyresoude, Luz Ardiden, few others) and have a new found massive respect for Mark Cavendish for being able to even get to the top of them on a treader. A few of the routes I was knackered just taking a motorbike up there!
There's a brilliant B&B just on the French side of the border a little way west of Andorra called Le Chapeau Bleu (Blue hat!) run by a guy called Ron - really great place, the first thing he does when you arrive is point you towards the cool box and tell you to help yourself. If you stay there then make sure to have dinner with them - I'd never heard of Baked Camembert before and it's incredible. In the morning he rides down to the bakery in the village to get fresh croissants and bread for the breakfast.
Whatever you do, don't look at property prices in the Pyrenees. Outside of the towns you can get properties for outrageously cheap prices compared to the UK - I nearly blew my redundancy money on my dream Farmhouse/ Barn to convert! (Reality kicked in and I realised I was probably going to need an income to support me...)
(You know I said earlier the only downside is that you find yourself going on about it to anyone who'll listen and many people who won't? See above.)