update price Observer is not working on cart page

Question

Here is the modules config file: app\etc\modules\Cart_Updates.xml

<?xml version="1.0" encoding="UTF-8"?>
  <config>
     <modules>
       <Cart_Updates>
         <codePool>local</codePool>
         <active>true</active>
       </Cart_Updates>
    </modules>
  </config>

Here is my config file : in app\code\local\Cart\Updates\etc\config.xml

<?xml version="1.0"?>
  <config>
   <modules>
     <Cart_Updates>
       <version>1.0.1</version>
     </Cart_Updates>
   </modules>
   <global>
       <models>
         <Cart_Updates>
           <class>Cart_Updates_Model</class>
         </Cart_Updates>
       </models>
       <events>
          <sales_quote_add_item>
              <observers>
                 <cart_updates_model_observer>
                    <type>singleton</type>
                    <class>Cart_Updates_Model_Observer</class>
                    <method>updatePrice</method>
                 </cart_updates_model_observer>
             </observers>
          </sales_quote_add_item>
      </events>
  </global>
 </config>

And here is the Observer: in app\code\local\Cart\Updates\Model\Observer.php

<?php

    class Cart_Updates_Model_Observer {

      public function modifyPrice(Varien_Event_Observer $observer) {
        //exit;
      $order = Mage::registry('current_order'); //For getting current order 
      echo $orderid = $order->getRealOrderId(); // For getting orderid
      $quote_item = $observer->getQuoteItem();
      $payment = 30; //add your custom product price here and do your logic here
      $quote_item->setOriginalCustomPrice($payment);
      $quote_item->save();
      return $this;
      }
      }
    ?>

Answer 1

here is code for updting the custom price

use this event checkout_cart_product_add_after

for current event

  $item->setCustomPrice($customprice);
  $item->setOriginalCustomPrice($customprice);
  $item->getProduct()->setIsSuperMode(true);

other method

   $product_id = $item->getProductId();
   $product=Mage::getModel('catalog/product')->load($product_id); 
   $item= Mage::getModel('sales/quote_item')->load($item->getId());
   $payment = 30;
   $item->setStoreId(Mage::app()->getStore()->getStoreId());
   $item->setCustomPrice($payment);
   $item->setOriginalCustomPrice($payment);
   $item->setProduct($product);  
   $item->save();