Qtla9111 you live in the Rolling Hills, area of Mexico. Monterrey, is to Mexico like Times Square is to Cheyenne, Wyoming. THERE ARE FEW "PROMOCIONES" of any significance out in the country. ISSSTE tiendas offer better than usual prices but a very limited selection. We are paying 14.22 pesos/liter for MAGNA. I don't give a damn how you cut it, even at an exchange rate of 13.30 to 1 THAT'S FOUR DOLLARS TEN CENTS PER GALLON for Magna, at a Pemex gasolinera. Let's not forget the pumps that have slight alterations or the bank/exchange vigorish of around 5%.
I could drive to Los Angeles to shop for food, to Houston, Texas for comistibles, and Seattle Washington for electrical power rates. But 99% of Mexico is a hell of a lot more expensive than what government AVERAGE prices lie about. How about you spending NINE HUNDRED and THIRTY THREE pesos for a 25 Kg cylinder of LPG, right at the plant? Oh sugar, the cylinder is only filled to 80% level to the liquid level bleed.
When RV'ers come to Mexico, they do not park next to the Bodega Aurrera at the beach. See all of the tens of thousands of corner Abarrotes? They are not there for the fun of it, an overwhelming majority of Mexicans walk to these tiny tiendas, and I can guarantee you these grocery markets have high prices.
I live Mexicano. I eat Mexican. My friends, my family are Mexican. I do not speak Ingles, although I write it. My friends cannot wait to go north and shop and fill with gasoline, and buy clothes, and gifts, and electronics. They marvel at the prices in the grocery stores - although for Mexicans bringing food, even canned and packaged food is difficult.
Life where vacationers go is a different universe than Mexico, or Monterrey or Zapopan. Life where most Mexicans live is the same way. Drop into the tienda the aborrotes near you and see how prices compare to Soriana, or Mega. You're going to be in for a rude shock. This is why people shop at tianguis or la mercado municipal.