It depends on your definition of 'amount of traffic'. With User roles in the integrated firewall (PEFNG), you can control/limit bandwidth (kbps) on a per client or per user-role basis. If you pick a role per SSID, then you can do the same per SSID.
For a traffic volume cap, where the connection is dropped after a number of Megabytes traffic volume, you will need to have an external server like ClearPass; or another RADIUS server that can change access based on time or data used.