$data['special'] = $this->currency->format($this->tax->calculate($product_info['special'], $product_info['tax_class_id'], $this->config->get('config_tax')), $this->session->data['currency']);

$data['discount_amount'] = $this->currency->format($this->tax->calculate(($product_info['price'] - $product_info['special']), $product_info['tax_class_id'], $this->config->get('config_tax')), $this->session->data['currency']);

<li>
<h2><?php echo $special; ?></h2>
</li>

<li class="discount_amount">
<?php echo 'Вы экономите '.$discount_amount; ?>
</li>

$special = $this->currency->format($this->tax->calculate($result['special'], $result['tax_class_id'], $this->config->get('config_tax')), $this->session->data['currency']);

$discount_amount = $this->currency->format($this->tax->calculate(($result['price'] - $result['special']), $result['tax_class_id'], $this->config->get('config_tax')), $this->session->data['currency']);

'price'       => $price,
'special'     => $special,

<span class="price-new"><?php echo $product['special']; ?></span> <span class="price-old"><?php echo $product['price']; ?></span>

<span class="discount_amount"><?php echo 'Вы экономите '.$product['discount_amount']; ?></span>