Let's correct the wrong information that has been posted so far.
1. You do not need to string a new c wire as there are adapters that avoid that expense:
https://www.amazon.com/Venstar-ACC04.../dp/B07RY3QG8J
2. Not all wifi thermostats require a c wire at all. Here is a highly rated, fairly inexpensive model:
https://www.amazon.com/Emerson-Therm.../dp/B01NB1OB0I
3. You do not need to hire someone to do this, it is quite simple.