It's a $4.99 monthly charge, but it's only for Comcast customers, so add that on top of your current monthly charges.
Comcast has announced they'll be launching a streaming service known as Xfinity Streampix this week. It's going to include the kinds of shows and movies you've come to expect from streaming services, but details on just what's going to be available aren't available yet.
The catch with this $4.99/mo service is that only Comcast customers will be able to access it, which makes the inexpensive pricing seem much less like a deal. Some Comcast packages will include the service for free - the higher end stuff of course - which should make a lot of customers sort of happy.
Depending on the selection and quality of the streams, this may convince Comcast customers to drop Netflix or Hulu in favor of the new service. These company specific services don't seem like the kind of thing that could bring the giants down, but they just might make a visible dent.