Borg tire stems

$100 isn't too bad. It's less than a tire shop wanted several years ago when I checked. $200 to do the same job, I declined. Ended up having it done by the auto hobby shop at the local Navy base. They did the work but wouldn't handle the RV, so I took the wheels off at home, loaded them in my van, hauled to the base, dropped off, came back, loaded up, back home, reinstalled. About $15 a wheel if my recall's right.

If you've recently bought tires, that shop might do the valves for less. An OP here took his valves to the shop he got his Michelins from and they installed the valves free, all six wheels.