class Order extends Model
{
  public function products() {
       return $this->belongsToMany('AppProduct', 'order_products')
                   ->withPivot('count', 'price', 'amount');
   }
}

class OrderProduct extends Model
{
    public function product() {
        return $this->belongsTo('AppProduct');
    }

    public function order() {
        return $this->belongsTo('AppOrder');
    }
}

select * from orders join (
    select order_id, sum(price) * count as sum from order_products group by order_id
) op on orders.id = op.order_id

$orders = Order::leftJoin('order_products', 'order_products.order_id', '=', 'orders.id')
     ->select('orders.*', DB::raw( 'sum( order_products.price * order_products.count) as `total`' ) )
     ->groupBy('orders.id')
     ->orderBy('total', 'DSC')
     ->get();

$orders = Order::all()
    ->transform(function($item) {
        $item->total_amount = $item->products->sum('amount');
        return $item;
    });