Number field Price multiply from user input?

Is there an example that could be provided for making this request a possibility? Just posting a link to the event subscriber source and long documentation to how event subscribers work isn't very helpful.

Going further, I believe it would be better if the number field could automatically multiply by the price of the field instead of making people custom code a solution that should be an obvious inclusion. Quantity and multiplying cost by that quantity is a very common scenario for checkout systems.

For anyone interested, I think I was able to get things situated:

mymodule/mymodule.services.yml

services:
  # Subscriber to the event we dispatch in hook_order_item.
  mymodule_order_item:
    class: '\Drupal\mymodule\EventSubscriber\OrderItemSubscriber'
    tags:
      - { name: 'event_subscriber' }

mymodule/src/EventSubscriber/OrderItemSubscriber.php

<?php

namespace Drupal\mymodule\EventSubscriber;

use Drupal\commerce_order\Entity\OrderItem;
use Drupal\webform_product\Event\OrderItemEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

/**
 * Class OrderItemSubscriber.
 *
 * @package Drupal\mymodule\EventSubscriber
 */
class OrderItemSubscriber implements EventSubscriberInterface {

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    return [
      // Static class constant => method on this class.
      OrderItemEvent::EVENT_NAME => 'onOrderItem',
    ];
  }

  /**
   * Subscribe to the order item event dispatched.
   *
   * @param \Drupal\webform_product\Event\OrderItemEvent $event
   *   Our custom event object.
   */
  public function onOrderItem(OrderItemEvent $event) {

    $webform = $event->webformSubmission->toArray();

    if ($webform['webform_id'][0]['target_id'] == 'mywebform_id') {
      $dinner_count = $event->webformSubmission->getElementData('dinner_count');
      if ($dinner_count > 0) {
        $event->orderItems[] = OrderItem::create([
          'type' => 'webform',
          'title' => 'Dinner guest count (' . $dinner_count . ' entries at $20 ea)',
          'quantity' => $dinner_count,
          'unit_price' => [
            'number' => 20,
            'currency_code' => 'USD',
          ],
        ]);
      }
    }
  }
}