1999 Mercury Sable Hard to Steer at slow speed

My steering is really hard turning when travelling at a slow speed, but it is especially hard when I parallel park. (feels like manual steering). I was looking on line and a problem with my vehicle is this exact problem, and it says that it requires the replacement of the control module and/or transmission-range sensors. Is this extremely costly? Does it mean the transmission needs to be replaced? I have no idea what this is.