I read on the official doc that to open a new channel it will cost $0.01. and it will last 2 hours.
so if I have 1000 concurrent users who use my site daily for 2 hours.
total cost will be 1000*$0.01 = 10$ daily.
Do they charge hourly too ?
i.e. if concurrent users use site daily for 4 hours, the resultant total cost will be 1000*0.01*2=$20 ?
It's only $0.01 per 100 channels, which equates to $0.0001 per channel. You can also change the lifetime of the channel token from 2 hours (you can make it greater or smaller), so you can effectively reuse channel tokens, depending on how they're used for your application.
So, if you leave the channel token lifetime at 2 hours, it would be '1000 * $0.0001 * 2 = $0.2` for the cost of channel token creation alone.
The rest of the cost, as you've indicated here, will depend on your bandwidth, CPU, and other server-side usage costs.
Seems like the calculation shown in https://developers.google.com/appengine/docs/billing is also wrong.