I'm taking my group of 55 students and parents to Arles in the south of France next year. If you have stayed in a hotel/hostel in this area with good prices and of a suitable size to accomodate my group, please let me know!
www.tourisme.ville-arles.fr has a list of hostels/hotels/B&Bs, etc. Auberge de Jeunesse has accommodation for 109, for example, and it's in the city centre.. Good Luck.