Hi guido,
Go in HikaShop > Configuration > Display, and set the option "Show discounted price" to "Display the discount amount".
Then in HikaShop > Display > Views, edit the view "Product / listing_price".
Add the line:
echo "<span class='hikashop_product_price_without_discount'>".$this->currencyHelper->format($this->element->prices[0]->price_value_without_discount,$price->price_currency_id)."</span>";
Just after:
foreach($this->row->prices as $price){
Then you can add texts before the price by adding:
JText::_('INITIAL_PRICE')
and add the translation in HikaShop > Configuration > Language, edit the language file and add (in this example) INITIAL_PRICE="initial price"