Costar un pastón

[poli]

It means costs an arm and a leg. I would like to know if it is international
or Spain-specific.

[JPablo]

I believe it is Spain specific. But it is not spelled "postón" but "pastón"

It comes from the word "pasta" (dough) meaning money, a lot of money... changed with an augmentative (pertaining to or productive of a form denoting increased size or intensity. In Spanish the augmentative suffix -ón is added to a word (as silla “chair”) to indicate increased size, as in sillón “armchair.”.)

I have also heard "costar un porrón [de dinero]"

[AngelicaDeAlquezar]

Title corrected.

It wouldn't be understood in Mexico. We might say an equivalent as "costar una lana" or "costar un lanal" or "costar una lanota".

[aleCcowaN]

From 39 instances in CREA for "pastón", 36 are from Spain and 3 from Argentina (where "pastón" means a couple of things: one meaning related to art and fashion, the other one related to masonry).

I suspect "pastón" is more like "a load of money" and not "an awful lot of money" as "an arm and a leg" ("un ojo de la cara") may suggest.

[JPablo]

El diccionario de argot de Espasa (Julia Sanmartín Sáenz) da, pastón mucho dinero. Le tocó un pastón en la lotería de Navidad.

Yo lo he oído y visto en España equivalente a:
Cuesta "un ojo de la cara" "Un riñón... y parte del otro"

Hay ejemplos a montones, como este que copio
... creo que es una guitarra ideal, y tampoco cuesta un pastón, cuesta lo suyo, pero tampoco como las js nuevas que cuestan más de 5.000 euracos.

(Me encanta los de los "euracos", rima con "atracos")