You might find better prices at Arab grocery stores or in stores that sell spices and condiments; a visit to the free market might be another option.
(aqui le dejo un resultado de mi busqueda, pero hay más: https://articulo.mercadolibre.com.ve/MLV-717648669-piedra-alumbre-1kg-_JM#polycard_client=search-nordic&position=5&search_layout=grid&type=item&tracking_id=3211d9b6-ec57-4733-a1ed-48de5a48e261)
Health and blessings