Aix-en-Provence offers 3500 rooms not to mention Airbnb. The average cost of hotel accommodation is around 110-120€ but there is a lot of hotel residencies, Airbnb rooms and apartments in the city center that are less (or more) expensive.
You can easily book
your room here
It is also possible (but less convenient and thus not recommended) to get rooms in Marseille (30 km). A shuttle service connects Aix to Marseille every 5 minutes at peak times (around 30-35 minutes from the Saint-Charles central station in Marseille to Aix-en-Provence bus station).