They make a service kit for the Sensor that is a new valve stem, often an entirely rubber (really rubber encased) valve stem replacement.
Problem is, if the metal steam has corroded so bad it totally seized, you're likely to damage/destroy the sensor trying to remove it.
The sensors usually only last 6-8 years anyway, you can get them much cheaper online at places like RockAuto. They are pre-programmed for your vehicle and work right out of the box (may take a few miles of driving for them to be recognized). I replaced all 4 of mine when I replaced my tires a few months ago, it cost me $32 a sensor from rockauto.
I did encounter a problem with one of the 4, no reading, I suspect I got water in the sensor when changing the tire. The next day I deflated the tire under 20 PSI and re-inflated it (suppose to reset the sensor) I suspect what it really did, was the rush of air in and out dried out the sensor and it started working just fine like the other 3 that started reading within 1 minute of starting the vehicle.
Of course the other problem with replacing the valve stem/sensor, you have to at least break the bead of the tire. I have access to tire changing machines to do it myself (although I have to pay a fee, still a lot less than a tire shop). So you're going to have to pay a tire shop to install it for you.