Has anyone ever tried getting to Biarritz and flying to Strasbourg from there? I appreciate all your responses!
Look at http://www.skyscanner.com/ for flights within Europe. It searches multiple websites and carriers (both budget airlines and "legacy" carriers like Air France). You then book directly with the airline. For the randomly chosen date of May 15, 2013, I see that all flights from Biarritz (BIQ) to Strasbourg (SXB) change in Paris Orly (ORY), but some are only 3 hours 10 minutes total, and under $200. This definitely looks better than trying to fly or train from San Sebastian the whole way. I don't know how easy or complicated it is to get from San Sebastian to BIQ airport, though - someone else here should, or you can check the airport's own website.
Thank you! I am now finding the same results. If anyone out there does know how to get from San Sebastian to Biarritz, I'd love to hear. I did get a taxi quote of 115 euros--steep, I thought!