We are spending a week in Valencia and then going to Biarritz.
the drop off fees are exorbitant. I suppose we could consider a train but it would be a nice scenic trip.
Any recommendations?

Your fee issue has to do with rental across the boarder. You have blocked out far more options than necessary.

Rent in Spain, drop off in Spain, such as San Sebastian.
Rent in France such as Perpignan, drop off in Biarritz.

Drop the car off in San Sebastian and then take the train Hendaye (it's a local commuter train) and transfer to another train to Biarritz.

Drop it off in San Sebastian and hop the train. Very easy to do.

May I suggest some notable lodgings in the vicinity of Biarritz...its been a favorite of our family for several years. It's located in the small Cliffside town of Bidart about 5 miles south of Biarritz...much quieter and not at all crowded like Biarritz...<b>Villa L'Arche</b>.

I'll post the web page below. The white sand beach below the Villa is sort of a lunar-scape with interesting rock formations all along its coast line. It's a pleasant hike along the beach to Biarritz.

http://www.villalarche.com/en/the-villa/

Be sure to request room with porch overlooking ocean/