I, too, have two of the SA 8300HD's. I'm told that the Motorola HD boxes are better, but Time Warner uses SA DVR's. If your cable company is Time Warner, figure on fees as follows: You must subscribe to Digital cable for starters. There is an additional fee for the HD Tier, plus a DVR fee if you choose to have a DVR. For each additional DVR, you'd have to pay another DVR fee plus a "Navigator Plus" fee.
I'm assuming you have either Comcast or Cox as a cable provider. Check the cable company's web site -- they usually publish rates on the web.