$5/month is just an introductory price, after the first year it goes way up, to $16.99/month. A cheaper "Mostly Music" is $10.99/month with a reduced 80 channels (looks like nothing I'd miss) that is satellite only, no streaming over the Internet.

I've liked listening to a handful of channels on Sirius XM when it's already been enabled in rental cars but it's not worth the price.