(1) I had a built in SAT Radio system installed in a BMW and it was pretty expensive to install. Can't remember the exact amount, but it was several hundred dollars.
(2) In several cars my family has owned we have purchased a small SAT Radio kit from Sirius XM and they work great. Probably less than $50 total invested. Comes with a mount choice of either on an air vent or with a peel and stick base or one that attaches to a sand bag type mount that sits on the dash. The radio works off existing FM radio. It will send the signal to an unused FM point on your tuner and you have the radio. It's really very simple to install. If I can do it, anyone can! Plugs into a cigarette lighter and the antenna wire can run from the magnetic antenna that sticks on the car top and the wire run in a very hidden way. Works great! Only thing is when you travel away from the FM tuner point you are using locally, you have to find another one that works, but it's quite simple and quick to do.
Satellite radio vehicle installation guide