I paid $250, but I had it "included" in the sales price. I think it is totaly worth it to get the XM straight through the RF. Much cleaner dashboard.
On the other hand, do get that 3 day free membership for web-XM and make sure you like the programming (becouase I don't, but thats just my exquisit-noncommercial taste
). I still keep it because I travel to the ski resorts everyweekend and its nice to good quality signal all through I70.
Just one last comment: you might loose XM signal in deep canyons.