After experiencing XM Satellite Radio in a friend's car, I decided to order one at my Toyota dealership in New Orleans. Note that you can see this unit at
http://www.coastaletech.com/xm_radio_in_prius.htm
Coastal Etech sells the unit for $410 and charges $50 to install it, if you want to drive to Florida (the Atlantic side, no less). My local Toyota dealership said it costs $265 and that they would install it for $150.
I ordered it, only to find out (after I left the car all day) that this was the 2001-2003 part; there was no listing in the master parts list for this XM Radio thingie. So I waited 3 weeks, while the parts people called first Houston (the zone office) and then the rest of the US, to find not only the price and availability, but also anyone who knew anything about it at all.
So far, nothing. I asked for and got a refund today, and I am waiting for some acknowledgement of the XM gadget advertised in the original car brochure.
Moral: the engineers who designed the 2004 Prius are geniuses; the people who run Toyota are morons. Oops! Was that tacky? How about "ill-prepared for transitioning to new technology," a kinder, gentler way of putting it.