When you call to cancel, if you do renew, they are VERY careful about making sure they tell you it will be auto renew at the then going rate. If this is a surprise or a mystery, you're simply not listening to them.
I use a credit card and always tell them to take the card off file and send me a bill. They also send an e-mail when my subscription is almost up. Never had a problem with being surprised with an auto renew.
I really don't like their business practices. They should just offer the service at a reasonable price in the first place. But, frankly, if you're caught off guard by an auto renew from Sirius, it's your own fault for not listening.