Comcast doesn't make it easy to change your service. Their web site says that you can "make changes to the Comcast services that you currently receive," but you really can't do it online.
After calling in to their customer service center, they admit that you can't drop a service online, you've got to call in.
So after calling in I got an explanation of their confusing pricing structure. On the web site it says the following for Digital Silver:
Digital Silver - ON DEMAND, 1 Premium Channel, Onscreen Guide. $76.70What you've got to do to determine the incremental cost of Digital Silver is to subtract the cost of Standard Cable and (1) Digital Cable box from the total Digital Silver price. $76.70 - ( 47.25 + 5.50 ) = $23.95.
Standard Cable - $47.25
I think it'd be a lot more user friendly to display your additional cost to add a premium service like HBO.