It USED TO BE that way. Now with smart phones, a store owner accesses the SHCP/SAT Banxico site while he is sipping coffee and calculating the percentage increase his labeling machine needs to be set at.
I am writing this from a large independent tienda de aborrotes y mercancia so I am a bit familiar with how things operate. Petroleos Mexicanos WILL NOT PERMIT gasoline and other comistibles to be "undervalued" as compared to with they way the fuel has been priced. They will jolt peso cost per liter upward.
Too many folks remember the way this economy USED to work when the peso was weakening. Way the hell and gone too many basic items are imported now, and you can bet your sweet butt, the proveedores have already raised peso prices.
Who suffers are poorer Mexicanos. The most infamous words a shocked traveler utters when his supposed "better values for the dollar" turn out to be empty night (higher peso prices found) "Why, why, why. they CAN'T DO THAT!"
Sure there will be a short delay between the sagging of the currency and imposed price increases but as a guess I would have to say the time lag is like 1.5% of what price increase lag was, back in the 80's.
The peso sagged 22 December 1994. By 1998 people were paying TWICE the price of gasoline IN DOLLARS. The Mexican government has zero accountability to the Mexican population.
I merely wonder how much the peso price of comistibles is going to jump. I would not be surprised to see $4.50 (yeah that's dollars) a (yeah that's gallons) gallon gasoline by the end of February.