I just spoke to comcast. They told me the cost for the 6200 (which replaces the 5100) is $5/mo. and the cost for the 6208 dvr is $9.995/mo. He also said if I swap the 5100 for a 6208, the increase per month is an additional $4.95/mo.
The sticker is the "delivery" fee. He quoted me $28 to deliver the unit and "install" it. I told them I paid a fee the last time, and they merely dropped off the unit and told me to install it after looking at my front projector/scaler et al. installation. The Comcast CSR guy said he was sorry to hear that, but would not waive the "delivery" charge. I would much rather go to Comcast (when it is convenient to me) and swap units, but that was also a no go. He said that HD installations must be installed by Comcast, due to its difficulty. I did not see the point in arguing that it is no more difficult to install a HD stb as compared to a SD stb. I just figured I'll call back later and try someone else.
Steve