IIRC its $500 or something for the lifetime. At least thats what it was when I worked at RadioShack over the holidays last year.
I've gotten to experince both systems, and I prefer Sirius.
XM: This is optional equipment on several Honda models, and I was able to check it out when I worked at a Honda dealership. As long as you didn't have anything over you, the signal was great. But if 2 tree branches were above you, you lost all signal. Whenever I'd go to the gas station and go under that "carport" thing, I'd lose all signal. Not sure if thats an XM problem, or if it was just crappy antennas that Honda put on the cars. Can any of you XM guys confirm/deny the reception issues? We also have XM at the office I work at, and our reception is usually good, but sometimes it cuts in and out for no reason.
Sirius: Our RadioShack store was inside a 2-story mall, and we were downstairs. Our antenna was right in the store, near the front (away form all windows/doors). We got crystal clear reception 24/7, even when there were huge storms outside. IMO, the selection of stations is better over at Sirius too. They have many more GOOD rock stations than XM (Squizz 48 is the only good rock one I've found on XM). Also, Sirius have NFL, NBA, NHL, Howard Stern, and NASCAR in 2007 (currently with XM. I've heard that Sirius may buy out XM's final year and take it 2006).
When the time comes, I'll be going with Sirius.
Hey, you don't need a Satellite-compatible deck with XM/Sirius, do you? I remember our Sirius "car kit" was a thing that you just selected an FM station to play on, but is that the same way with XM?