opencart — разница между специальной ценой и ценой по умолчанию

echo substr_replace(preg_replace("/[^0-9?]/si","",$products[$j]['price'])-preg_replace("/[^0-9?]/si","",$products[$j]['special']),substr(preg_replace("/[^0-9?]/si","",$products[$j]['price'])-preg_replace("/[^0-9?]/si","",$products[$j]['special']),-4,1).",",-4,1)." р.";