What are the options for getting from the San Sebastian Airport to the Hendaye train station ?
Looks like a Taxi
It looks like Bus E23 and E28 will get you to Irun, which is just across the border from Hendaye.
I can't make out exactly where in Irun it stops.
http://www.aena.es/en/san-sebastian-airport/public-transport.html
The Hendaye rail station might be walkable from the bus stop in Irun, but I'm not sure. I'd print out a map from Google Maps and carry it with me. Best to avoid what looks like a very expensive, if short, taxi ride if possible.