score:4
I just checked airbnb.com and found accommodation for under 40 euros in August. It seems, indeed, that there are either very few or no hostels in Cannes, if a hostel is an accommodation with dorms. I suppose flashy Cannes does not have much of an interest in the lower end of the tourism industry.
Nearby Nice does have hostels, or rather, accommodations with dorms, but these are not too cheap, starting at roughly 30 euros per night per bed.
Upvote:6
August the traditional "everyone go on holiday" month in France (and Italy). Hence they are probably very booked up.
Another theory is that Cannes might be more higher class tourist destination and there might be no hostels. Try nearby towns/cities. Sometimes the train between these places is very fast and cheap. I got a single train ticket from Monaco to Nice for about €3 and it only took 45 minutes. Why not stay outside Cannes?