WooCommece cost price custom field

functions.php

// Cost price
add_action('woocommerce_product_options_pricing', 'cost_price');
function cost_price() {
    woocommerce_wp_text_input(
        array(
	            'id'	=> '_cost_price', 
	            'class'	=> 'wc_input_price short', 
	            'label'	=> __('Cost price', 'woocommerce').' ('.get_woocommerce_currency_symbol().')',
	            'type'	=> 'text',
	     )
    );
}

add_action('woocommerce_process_product_meta_simple', 'save_cost_price');
function save_cost_price($post_id) {
    global $wpdb, $woocommerce, $woocommerce_errors;
    $cost_price = $_POST['_cost_price'];
    update_post_meta($post_id, '_cost_price',  esc_attr($_POST['_cost_price']));  
}