Translate "back in the day"

Question

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?

Answer 1

It isn't the exact translation, but a good equivalent could be

Érase una vez ...

It's usually used in the beginning of a fairy tale though, which is why most people will probably downvote this.

If you want to get literal in your translation, you could say

Durante los antiguos tiempos ....

Which is more equivalent to

Back in the old days

To say Back in the day suggests something with an indefinite duration and a slightly defined termination point. Like,

Back in the day we used to play volleyball`

Back in the day cell phones didn't exist.

Back in the day our dogs walked themselves.

It's the same as saying

In the past, our dogs walked themselves

So the translation would use the imperfect

En el pasado nuestros perros se paseaban a sí mismos.

Answer 2

Maybe, in Spanish you could say:

Hace tiempo el trigo valía cien dólares por tonelada
Tiempo atrás, el trigo valía cien dólares la tonelada

So, "back in the day" could be translated to:

Hace tiempo [better]

Or

Tiempo atrás

Answer 3

You can say antiguamente too. I don't know which translation is more likely to be used by a Mexican, because I'm Chilean...

Antiguamente, el trigo valía 100 dólares la tonelada.