During the beta period, the service is available for free. Once it comes out of beta, developers will have to pay $0.40 per million for the first 100 million API calls each month. Users who need to send more messages will pay $0.25 per million for the next 2.4 billion operations (that’s about 1,000 messages per second) and $0.05 per million for messages above that.
http://techcrunch.com/2015/03/04/googles-cloud-pubsub-real-t...