It's quite a few years since we were in Biarritz but it is a great destination with lots to do in the area with its' proximity to the Pyrenees. Some lovely towns to explore: St Jean de Luz & to San Sebastian across the border.
We were caravanning at the time but don't remember things being any more expensive there than other parts of France. As with anywhere there will always be expensive options but plenty of cheaper Bistro type places & I wouldn't be put of by fears of high prices. Have you explored private rentals ( Owners Direct, Holidaylettings etc?) as you can budget more easily -- maybe make your own breakfast & lunch & eat out at night?)
Beaches on that Atlantic coast are fantastic but be warned very high seas: hence a favourite destination of surfers so always swim where there are life guards.
I'd recommend the area. Hope this helps