Just before the account is up for renewal, I always call to cancel. This is for XM not Sirius. Yes they merged, but they're still seperate.
Since I signed up in '06 I've always been offered $77 for a year or $20 for 5 months.
Say you wish to cancel, it's too expensive. The woman offered me 3 deals this year.
1. 5 months for $20.00
2. 6 months for $38.00
3. 1 year for $77.00
I went with the year to save the hassle of calling again in 5 months. She waived all royalty fees and taxes. It was $77.00 plus 2 bucks invoice fee (not giving them my credit card).