I don’t know when it happened, but the RCA airport shuttle (line n° 210) timetable has been changed. The last one now leaves Cannes from close to the Mairie/town hall at 7pm! That’s right, after 19h, you will have to fork out €70-80 to get to the airport from Cannes. The airport website still lists the last shuttle at 8pm (which is already way too early for a public service in my opinion). But the timetable at the bus stop is clear: 7pm. The bus n° 200 that goes through Antibes does run until 8.10pm (8.30 on Sundays and holidays), but it takes between an hour and 90 minutes to get to the airport and stops at Terminal 1. For the latest timetables, check the RCA timetable (in French).
If you intend to leave Cannes after 7pm, I strongly recommend planning ahead and sharing a cab.
You can book your shuttle service at http://www.nice-airport-shuttle.com