PCR lab tests (not rapid antigen tests) for COVID

[Peter]

To partially answer my own question, I've learned that the Lapcic laboratory will do the most accurate, PCR test (with a result in 48-72 hours) for 2,000 pesos. They will also do the less sensitive, rapid antigen test (same-day result) for 850 pesos.
Here is their link: http://www.lapcic.mx/covid-19/