As far as I know, Sia is based on POW - you're right.

At http://siapulse.com/ you can see some interesting stats. You are also right about the extremely cheap price - a TB for a month is about $1.30. I think that is due to under-utilization of the network, so hoster are still competing hard with the price.

I'll shortly try Sia out so I can answer more questions about it.