Drupal Commerce - Retrieve cart value
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'];