why do you not just write your on broadcast system.. it really would not be to hard and you could cut that cost out of your running fees.
You were definitely right on this one... I've migrated off of PubNub to my own deployment of Slanger/Pusher. Costs are now down to ~$60 a month to be able to support everyone for all channels of data. Plus we still have the benefit of having several clients available for connecting provided by Pusher.
https://github.com/stevegraham/slangerhttp://pusher.com/