My dealer quoted me $649 installed for the XM option. They charged me 2 hours labor, although the service manager mentioned that they can (and often do) take upwards of 4+ hours to install. I'm not surprised after looking at the install instructions.
Although I currently have a portable Sirius receiver in my Insight, I opted for the XM option in the HCH. I like the fact that it's integrated into the car's hands-free system (I'm a notorious channel-flipper), and that it will be covered by the Honda warranty.

The Sirius radio will go into my wife's Pilot or in my Triumph, if I ever get a radio for it.