Prices vary from city to city and state to state. Here in Monterrey, the average price is 19.99 but fuel can be found at Walmart gas stations at 19.56.
It is important to use a Mexican fuel price app to find pricing. I don't know of a webpage similar to GasBuddy which would be useful.
We use Gasoapp but it is only good for a 20 km range. However, I believe you can put a location other than yours and do the same thing.
Fortunately, here in Monterrey, people are consumer conscious and are buying fuel by price which was not part of our culture before the Mexican energy reform. You see long lines at stations with lower prices.
I've seen prices as much as 2 pesos difference depending on the part of the country I have traveled in excluding competitive border pricing as low as 14.25 per liter.
