Hi all.  I just bought a used '08 Edge (and I LOVE it)!  I want to add Sirius radio if at all possible, and am curious how to best go about this.  Currently, the system is the basic CD/MP3 arrangement.  What are my options on adding Sirius?  Would it be better to purchase a Sirius radio and have it installed someplace like Best Buy, or go with a Ford factory option?  What are the costs of each?   
  
Thanks for your help!