Asking whether Roku is free is like asking whether TV is free. After you pay for a TV, you can watch some stuff for free (usually with commercials). This stuff typically comes over the air, or possibly you hook up to some community/building/university cable system. However, you can also connect it to commercial cable, satellite etc. and likely be paying monthly. Roku is basically the same. A lot of stuff (most I think) is free (usually with commercials) but some stuff is paid/subscription. Without naming what you're getting, no one will have any idea of what your monthly charge (if any) should be. It's worth checking the fee structure (if any) of any channel before you add it.
And, yes, it is possible to call "some guy" on the phone and have him set up your Roku, and he'll charge you whatever he wants to do something that you can do yourself for free. No one in this thread has said that they actually did that but it can happen. Neither of the posters have really given any details so you just get "general possibilities" as responses.
