Having the modem on is not what you pay for. You pay for using the service each month. it is a flat fee, which means no matter how much or little you use it the amount is the same. You could do the following to lower the cost of your cable bill:
-Get rid of movie channels. I did this myself years ago because I watched maybe one or two movies a month, which certainly doesn't justify the cost.
-Consider downgrading to a smaller package. If you have the premium package, but don't even watch half the channels, whats the point?
-Consider getting rid of any other extras or premiums you may have, especially if you don't use them, or use them seldomly.