I have searched flights and the ones at decent time of day are quite expensive. Any other recommendations for traveling between these two cities. I cannot find train sxhedules as they aren't posted for late October yet.
According to RometoRio.com the fastest way is fly Seville to Bilbao and take the bus to San Seb. Checking flights on Google flights brought up fares from $51 to $158 depending on the date and particular flight. Trains seem to be more expensive and take longer.
I'm not surprised by Phillip's results. www.skyscanner.com is another useful search engine for flight specifics. A Coruna also has an airport.
Trains can be done with "one" connection, like this, but that change also requires a local train or metro between stations in Madrid:
Sevilla Santa Justa Fr, 24.06.16 dep 11:45 AVE 2111
Madrid-Puerta de Atocha Fr, 24.06.16 arr 14:15
transfer 45 min. by local trains
Madrid-Chamartin Fr, 24.06.16 dep 15:00 A 4145
Santiago de Compostela Fr, 24.06.16 arr 20:19
OR
Sevilla Santa Justa Fr, 24.06.16 dep 15:00 A 2135
Madrid-Puerta de Atocha Fr, 24.06.16 arr 17:48
transfer 45 min.by local trains
Madrid-Chamartin Fr, 24.06.16 dep 18:50 A 4185
Santiago de Compostela Fr, 24.06.16 arr 23:59
Not going to Santiago de Compostela this trip but would love to return there. This all started when my non stop Vueling flight from Seville to Bilbao was moved from early afternoon to late at night. I asked for a refund as I still would have to drive from Bilboa to San Sebastián which is not an option. I do use sky scanner and Google Flights too. Maybe a high speed train to Madrid and then a non stop flight to San Sebastian's airport? Thanks for your help.
Sorry that I fixated my answer on the wrong "S" town. Train schedules to San Sebastian are similar, afternoon departures with "one" connection but a change of train station in Madrid and total travel time of 9 hours. These are not likely to change for October. I don't see any benefit to switching to a flight from Madrid, with the associated airport connection and check-in time.
Last year we took the train from Seville to San Sebastian. There is a direct, fast train from Seville to Zaragoza. Then a slowr but nice train to San Sebastian. Trains are the way to travel in Spain. Try RailEuro.com. Aloha