WordPress doesn't save custom meta box

Hello
I’m new to wordpress and this is my first post to this forum.
I’m building a simple theme for a virtual computers store. The theme is very simple and it contains a custom post type called “product” to add a new product.
I added a custom meta box the this post type called price to add the price of the product.
The problem is when I save the post (product) or update it the price is not saved to the database.
Here is the code to add the custom meta box for the price:

<?php
function cp_product_meta_price_box(){
		add_meta_box('cp_product_price', __('Price','cptheme'), 'cp_product_meta_price_fields','cp_product', 'side', 'core');
	}
	add_action('add_meta_boxes', 'cp_product_meta_price_box');

function cp_product_meta_price_fields($post){
	wp_nonce_field(plugin_basename(__FILE__), 'cp_product_meta_noncename');

	$price = get_post_meta($post->ID, 'cp_product_price', true);
?>
	<p><label for="cp_product_price">Price: </label><input type="text" name="cp_product_price" id="cp_product_price" value="<?php echo esc_attr($price); ?>" ></p>
<?php
}	

function cp_product_meta_price_save($post_id, $post){

	if(defined('DOING_AUTOSAVE')&& DOING_AUTOSAVE){
		return $post_id;
	}

	if(!isset($_POST['cp_product_meta_noncename']) || !wp_verify_nonce($_POST['cp_product_meta_noncename'], basename(__FILE__))){
		return $post_id;
	}

	global $post;
	$post_type = get_post_type_object($post->post_type);

	if(!current_user_can($post_type->cap->edit_post, $post_id)){
		echo 'ERROR';
		return $post_id;
	}

	$metadata['cp_product_price'] = (isset($_POST['cp_product_price'])?$_POST['cp_product_price']: '');
//		echo "<h1> Price is : $metadata['cp_product_price']</h1>";

	foreach($metadata as $key => $value){
		$current_value = get_post_meta($post->ID, $key, true);

		if( $value && '' == $current_value)
			add_post_meta($post->ID, $key, $value, true);
		elseif( $value && $value!= $current_value)
			update_post_meta($post->ID, $key, $value);
		elseif(''==$value && $current_value)
			delete_post_meta($post->ID, $key, $current_value);
	}

}
add_action('save_post','cp_product_meta_price_save',10,2);

Please could you tell me what is the problem in this code. I tried to find the problem for 2 days and found nothing wrong but I don’t know why it’s not working.

Thank you