[This followup was posted to alt.autos.ford and a copy was sent to the
cited author.]

If so, what would be the estimated cost of servicing it since my car is currently out of warranty?

The temperature sensor is mounted behind some small slots in the control
panel (sort of on the left side on my 2000). In turn, there is a hose
connect from that to the fan (upper-right of the passenger side
footwell) to provide some suction. Make certain there is nothing
blocking the intake, and that the hose (it's about 1" diameter white on
my car) is not smashed or disconnected.

If you set the temperature to 90, it should override the sensor and
provide full hot. If it's still not hot, then either the blend door is
not working properly, or your heater core is clogged.

You may also want to double-check the MicronAir cabin air filter, too.
It sits horizontally just below the passenger side of the windshield,
under the cowl, and leaves and sticks tend to clog it up, restricting
airflow. The owners manual should show how to check it. Be VERY careful
with the water shield above it. If it has the flap on the side to direct
water away, and you tear it off, you need to replace it or water will
leak into the car!!!