How does billing work for Sirius Internet Premium? Can you sign up for a year and get a discount, or is it always just $2.99 per month?

I'm in the process of renewing my membership, and it gives you the option of upgrading to Premium, or staying with regular for free, but the difference in payment is only $1. So I'm assuming that the Internet Premium is billed monthly, separately, but then what's the dollar difference for?