Consider the following sentence:
Back in the day wheat used to be 100 dollars a ton.
Here, "back in the day" is just another way of saying something like "once upon a time" or "back then" or "there was a time when". What would be the most natural to say it in Spanish?
Off the Internet, I have noted the following alternatives:
En aquel entonces el trigo valía cien dólares por tonelada.
En ese entonces el trigo valía cien dólares por tonelada.
Por antaño el trigo valía cien dólares por tonelada.
En tiempos pasados el trigo valía cien dólares por tonelada.
Which of the above is the most likely one to be used by a native (Mexican, in particular) speaker? Or, is there yet another translation which is more intuitive/colloquial than the above three?