Hi,
You'll have to add a custom product field via the menu Display>custom field in order to enter the original price in your option variant and then edit the file "option" of the view "product" via the menu Display>views and add the display of the custom field next to the price.
So instead of:
$text.=' ( '.($positive?'+ ':'').$this->currencyHelper->format($price,$ok->price_currency_id).' )';
you can have:
$text.=' '.($positive?'+ ':'').$this->currencyHelper->format($price,$ok->price_currency_id).' <s>'.$variant->custom_field.'</s>';
where custom_field is to be replaced by the column name of the custom field.