Correct, you do NOT pay the modem rental if you work with them to get it off your account. Usually this requires dropping off the modem at a local office, make sure you get a slip for proof that it was returned, or you request a box to ship it back. Then your free to use your own modem at no additional cost.
I looked up the Cisco CM100, i see no problem using that for your tier, its a DOCSIS 2.0 compliant modem. However, i was merely pointing out that if you have D3 availability in your area that even at your tier channel bonding with a D3 modem will be an improvement and you will get more of what you pay for. Streaming those movies will even work better at 3mbps when your not congesting a single channel downstream.
I know customers here on the intro package that bought a Surfboard modem at the local Wal-Mart, its a SB6121, they didnt want to pay modem rental i guess, but the point is it even makes their service much faster and more responsive.