This is the output of your array, when unserialized:
Array
(
[0] => Array
(
[price] => Array
(
[value] => 17300
[original] => 19800
)
[custom_tax_inside] =>
[custom_tax_page] =>
[city_mpg] => Array
(
[value] => 5.7
)
[highway_mpg] => Array
(
[value] => 4.6
)
[custom_badge] => Venduta
=> https://www.youtube.com/watch?v=IBCOAumh6aI
[short_desc] =>
)
)
So, to access the price, you have to change your shortcode to this:
function dmc_prezzo() {
$postid = get_the_ID(); // get id from post in loop
$meta_data = get_post_meta($postid,'listing_options'); // select array
return $meta_data['listing_options']['price']['value'] . ' ' . $meta_data['listing_options']['price']['original']; // extract keys
}
add_shortcode('dmcprezzo', 'dmc_prezzo'); //usage [dmcprezzo]
It would be better if you’ve posted the entire serialized data, I’m not sure if it’s not nested.