You really need to indicate what services you want the TV in the other room to receive. Example if all you want is the local channels (assuming you have a TV with a QAM, digital tuner) all you need to do is provide a splitter to the cable and run a new cable to the TV. If you want to be able to receive the extended basic (digital starter) channels then you will need a DTA box prior to the new TV (you should be eligible for two free per household and there isn't a monthly charge). If you want higher service then you would need a Converter box, and assuming you are already using one on another TV, you would be charged in the neighborhood of $10.00 per month..
I'm not sure that's true, even after the digital transition, current type TVs should work on basic cable with no bells and whistles. Comcast will add an outlet into another room ($65 locally). If you did NOT add a box there would be no addl monthly charges.