It sounds like Cycling-rentals.com, that dduroy suggested, may not be a bad way to go. It sounds especially tempting, since they offer all the extra equipment and phone.
Jane and I recently rode bikes from Barcelona to Leon. We were planning a 14 country bike ride over a five and a half month journey. I wanted to visit the places my dad was in during WW II. He was a paratrooper with the 82nd Airborne. I'm writing a book about his adventures
http://WhereDadDroppedIn.com . Jane wrote the book, Women of the Way,
http://tinyurl.com/7knb7p9 and decided that it might be interesting to explore doing a book about bicycle riding on a Camino. For us, the ride from Barcelona to Santiago, was not a good choice. That route, to Leon anyway, is a real challenge. We did it in May, and there is a steady, and very, very strong wind out of the north for the entire route.
There were actually a few places where we were going down a substantial downhill section and had the bikes in the lowest gear and had to pedal, otherwise, we'd just stop. We were riding touring bikes with 700C-35 tires, not mountain bikes. Were I to ride in Spain again, at least for the Camino, I would choose a mountain bike and ride the off-road sections as much as possible. The route from Barcelona is mostly on very busy, high-traffic roads, and most of that traffic is trucks.
Admittedly, the drivers were quite good and cautious, but there were NO shoulders, very deep drainage ditches adjacent to the roads edge and the albergues, were few and far between. Even with all that, the wind was the worst part of the journey.
We stopped riding at Leon, even though Santiago was our destination, because Jane had a very bad crash and ended up taking a ride in an ambulance. There is so much cobblestone in Spain that the road bikes can be a challenge. Jane crashed due to an encounter with unfriendly cobblestone. She had something like twenty stitches in her knee and the doctors advised her not to ride the bike for at least a month. We purchased the bikes new at Tomas Domingo
http://www.tomasdomingo.com/ in Barcelona and were very pleased with the bikes. We decided to store them in Santiago and walk the Portuguese Camino from Lisbon, she was able to walk just fine. When we returned to Santiago, it was obvious she couldn't ride yet, even though it had been a month, so we shipped the bikes home. To find a buyer for expensive machines, on short notice, was almost out of the question.
We shipped them home, for a VERY reasonable price, with Mail Boxes Etc.
http://www.mbe.es/index.php?id=1822&store=SPMBE0127 and they were fabulous. Jane is fluent in Spanish, but not to worry, everyone there spoke excellent English. I highly recommend them for shipping bikes from Santiago. The bikes arrived in great shape.
We continued on our journey with backpacks, trains, buses and ferries. We just returned two weeks ago and I know Jane will working on some books about the journey. Would we bike there again? The jury is still out for Jane, but I would. However, I'd do it with a mountain bike and try to trail ride as much as possible.