About 10,000 munster supporters have just come back from there - they were charged €7 a pint and €40 for a steak dinner - a bit over priced by the sounds of things. Though I'd say this was only for the match week-end. If you search through the fourums on munsterrugby.ie and musterfans.com you might some interesting links as there was a lot there in the week preceding the match.
For the Munster match, I stayed in San Sebastian (Donostia to the Basques) and it was the best decision. SS is fantastic and only 15miles from Biarritz. It is far cheaper, friendlier, more beautiful and to be irish in SS is very good (we did a good PR job !) To be honest, I can't wait to go back there again. The food is fantastic and in the Old Town there are loads of Tapas bars where the idea is to have a drink and a tapas in one, then another and so on. [broken link removed] http://www.sansebastianturismo.com/ingles/indexi.htm
p.s. there is a Carrefour on the outskirts of SS coming from Biarritz where the Petrol/Alcohol and food are cheaper than France....it's where all the locals from Biarritz go to shop.