TPMS Problem

My mother's 06 Prius has four seized valve caps. I've taken it to a tire shop and the dealership because the tire shop said that they wouldn't risk breaking the sensor on any of the tires. They quoted me $70 apiece for the sensors. So I went to the dealership. Now I'm getting quoted $117 apiece, which jives with what I'm seeing online.

Now the big question...

Can't they just replace the bloody valve stems? I mean, I see places selling TMPS stems and $14 apiece is a bit easier to swallow than eight times as much. Of course, if they could, why wouldn't the dealership be offering them as an alternative? I just want a second opinion.

Any and all help is greatly appreciated! Thanks!

Hey, i had a similar problem but i went to whytpms.com and was able to figure out y everything works the way it does.
:iceslolan