How much would it cost for an electrician to fish a wire?

I need to wire an xbox 360 ethernet cord from the room above my router. I am wondering how much it would cost to get an electrician to come out and fish the wire from the room above to the room below it and drill a hole so i can connect it to my router. My house is already built and not in the process. (i was told it is always harder to wire a house when its built) Please give imformative responses.