To replace the torque converter the transmission has to be removed. A genuine Ford torque converter is about $300, transmission shop may source a reputable one cheaper, labor to R+R transmission according to my labor guide is about 8 to 8.5 hours work. I would be concerned about the transmission itself once its out it may be advisable to overhaul it.
i agree with both answers, the question i have is, why are you replacing the converter ? there is a common issue with the AX4N, and AX4S trans in the Taurus that causes no forward and no reverse gears. The converter splines can strip out or the transmission pump drive shaft will break. if that is the concern you will need to tear down and replace the drive shaft for the pump, as it has probly been damaged, and at that point you are most of the way there for a rebuild. i would weigh the cost of rebuilt/reman trans verses the mileage and so forth, if you are over 80k miles, look into rebuilding, or replacing the unit.