I last went to EAS about 2 years ago, it was late at night, and I remember seeing 3 taxis there. I was being collected, but I had the impression the taxi drivers were actually sharing out the passengers to ensure everyone was accounted for, and presumably it would have saved the passengers a bit on the steep taxi fares in north Spain.

Taxis Hondarribia: 943 641 256 / 682 923 685 according to:
http://www.aena.es/en/san-sebastian-airport/taxi.html

Because it is so far out of town, I came to the conclusion that BIO is the more useful airport for San Sebastián.

As far as I am concerned, the whole of Spain is safe, and certainly that area is, subject to taking the usual modest but sensible precautions.