Is there a direct bus/train between these 2 cities? Does anyone have info about timetables/prices? I was thinking about visiting them both in the next week or 2 but maybe it isn't a good idea while the weather isn't great?

In the past we have flown into Biarritz, lovely seaside town with great beaches and a top surfing area, we have then got the TGV down to Hendaye (20 mins) and then walked to the FEVE station (10 yards) directly linking Donostia and Bilbao is directly outside Hendaye station, the rail connections from Hendaye to Biarritz are ok on weekdays but can be a bit ropey on a weekend

ta luego

Last September I took a day trip by bus from San Sebastian to Biarritz. Autobuses PESA had two buses daily (Except Sunday). I took the bus at 9:00 and I believe there was another bus at 2:30. The trip took about one hour.