Buy your own modem at amazon.com, comcast charged you $3-$5 per month for using their own modem.
Motorola SB6120 is $76.49 or you can buy
Motorola SB 5101 for $50.00
If you need a phone line as well, buy
Obi 110 for $50, it's using google voice and it's free.
Just order it through the internet and call them every 6 months to renew the deal