Even a couple of dollars more for a contractor is a lot when a thermostatic valve doesn’t add any value.
You can get inexpensive tankless water heaters.
You want to open the hot valve 100% until the hot water comes because it conserves water. You want to clear out the hot water line as fast as possible. Turning it to 70% just takes longer to heat up and you’re just dumping cold water out for no reason.