Biarritz will be good. Non-surfing partners always love it.
I've stayed at Palym Hotel rue de vieux port a few times and Carlina Lodge overlooking Cote des Basques a few times too. Just looked at their websites and Carlina seems booked out for July and the Palym prices seem to have rocketed. Was about 30e a night when I last went in 2005.
Theres a couple of Etap hotels near the airport that will be nice and cheap, stayed there too, only 5 mins to town.
If its flat then there's good hill walking, nice town and Bayonne is nice. If you have a car then Pamplona is just an hour or so drive and that is one big party. My tip for Pamplona is to drive to just outside the old city, park there and walk into the city (about 20mins) - one of the biggest all night parties (subject to your views on the bull run) in Europe. Kip in your car when the party ends at about 9am and write off the day. First time we went there me and the mates just hiked from the Santander ferry, booked our rucksacks in old town store they set up and kipped in the park in the day, the car tip was done in later years.
San Sebastian is a great city too just 40-50 mins from Biarritz. Read recently its the most expensive city in Spain for accomodation. Fairly decent surfing there when its on.
You're too deep Camel..its Indo not Margaret River