gistfile1.php

<?php

// Register the column
function price_column_register( $columns ) {
	$columns['price'] = __( 'Price', 'my-plugin' );
 
	return $columns;
}
add_filter( 'manage_edit-post_columns', 'price_column_register' );

// Display the column content
function price_column_display( $column_name, $post_id ) {
	if ( 'price' != $column_name )
		return;
 
	$price = get_post_meta($post_id, 'price', true);
	if ( !$price )
		$price = '<em>' . __( 'undefined', 'my-plugin' ) . '</em>';
 
	echo $price;
}
add_action( 'manage_posts_custom_column', 'price_column_display', 10, 2 );

// Register the column as sortable
function price_column_register_sortable( $columns ) {
	$columns['price'] = 'price';
 
	return $columns;
}
add_filter( 'manage_edit-post_sortable_columns', 'price_column_register_sortable' );

function price_column_orderby( $vars ) {
	if ( isset( $vars['orderby'] ) && 'price' == $vars['orderby'] ) {
		$vars = array_merge( $vars, array(
			'meta_key' => 'price',
			'orderby' => 'meta_value_num'
		) );
	}
 
	return $vars;
}
add_filter( 'request', 'price_column_orderby' );