Hi,
In the product / listing_price.php view file, you'll fine this line:
echo '<span class="hikashop_product_price_per_unit_x">'.JText::sprintf('PER_UNIT_AT_LEAST_X_BOUGHT',$price->price_min_quantity).'</span>';
You could change it to :
if(isset($this->element->main)) echo '<span class="hikashop_product_price_per_unit_x">'.JText::sprintf($this->row->salemethod.'_AT_LEAST_X_BOUGHT',$price->price_min_quantity).'</span>';
elseif(isset($this->row)) echo '<span class="hikashop_product_price_per_unit_x">'.JText::sprintf($this->row->salemethod.'_AT_LEAST_X_BOUGHT',$price->price_min_quantity).'</span>';
else echo '<span class="hikashop_product_price_per_unit_x">'.JText::sprintf($this->row->salemethod.'_AT_LEAST_X_BOUGHT',$price->price_min_quantity).'</span>';
And then you can add your translation overrides like:
PER_PACK_AT_LEAST_X_BOUGHT="per pack for buying at least %s"
where you would change "per pack" and "PER_PACK" based on what you have in your salemethod custom product field.