Craft Commerce Product Options that increase price, but do NOT affect stock
Worked it out!
Putting this in a custom module should do the trick..., obviously changing the price modifier and option name to your needs.
        Event::on(
            LineItems::class,
            LineItems::EVENT_POPULATE_LINE_ITEM,
            function(LineItemEvent $event) {
                // @var LineItem $lineItem
                $lineItem = $event-&gt;lineItem;
                // @var bool $isNew
                $isNew = $event-&gt;isNew;

                if (isset($lineItem-&gt;options['giftWrapped']) &amp;&amp; $lineItem-&gt;options['giftWrapped'] == 'yes') {
                    $lineItem-&gt;price += 20;
                }
            }
        );