The best guide, always, to find accommodations is the red guide of Michelin.
You should have no problem in finding a place for under $100. The only
concern might be around May 24, Ascension Day, a general holiday weekend
For more information, you might want to visit our site, which has articles on Arles (Roman ruins) and Les Baux-de-Provence (in the archives). Also plenty of links to other sites.
Frieda Lekkerkerker http://www.aboutprovence.com