Drupal Commerce - Retrieve cart value I'm trying to create a popup notification on a route that shows the current cart value (subtotal) and notifies users to add $X.XX to receive free shipping.

I have extended a route to add new functionality but I'm unsure whether a hook or service would be best/appropriate.  I can't seem to find any documentation on cart value--I can see some functions for retrieving quantity of items and seemingly could calculate the price by retrieving the prices for each individual item but research isn't bringing up much.

I see information regarding Order Totals but one would seemingly have to finish the order process in order to retrieve that data.  I'm trying to grab cart value when a user goes to the /cart page.  

I'm not asking for anything specific, just a pointer in the right direction.  Thank you.
If you know the store id and order type then 

$store_id = 1;
$order_type = 'default';
$cart_manager = \Drupal::service('commerce_cart.cart_manager');
$cart_provider = \Drupal::service('commerce_cart.cart_provider');
$entity_manager = \Drupal::entityManager();
$store = $entity_manager-&gt;getStorage('commerce_store')-&gt;load($store_id); 
$cart = $cart_provider-&gt;getCart($order_type, $store);
$cart-&gt;get('total_price')-&gt;getValue()[0]['number'];