Computer Repair Sacramento CA - Jonathan Warner Knowledge Base: How to replace Comcast Modem with my own. Comcast used to charge about 1.50 per month to rent a modem. Did you know Comcast currently charges 7.99 per month to rent a modem but a Comcast approved cable modem can be bought for less than 40.00? If you switch out your rental with one you own, even if you have to replace it yearly - which is unlikely, you will save money!