add_action( 'woocommerce_before_calculate_totals', 'extra_price_add_custom_price', 9999, 1 );
function extra_price_add_custom_price( $cart ) {
    if ( is_admin() && !defined('DOING_AJAX') )
        return;

    foreach ( $cart->get_cart() as $cart_item ) {
            echo $cart_item['data']->price; // this gives the price that i want but

        if( isset($cart_item['custom_data']['new_price']) ){
            $cart_item['data']->set_price( floatval($cart_item['custom_data']['new_price']) ); // here price is not updated
        }
    }
}