How to get the total number of meta_values based on a custom post type?

There may not be a need for a custom query, but I’d recommend it rather than hitting the database:
– once for the WP_Query
– once more for each post entry

And then manually working out the math in PHP. Do it all at once with one MySQL statement.

select sum(PM.meta_value) from wp_postmeta PM
join wp_posts P on P.ID = PM.post_id
where P.post_type="page"
    and PM.meta_key='test'

With your code above, replace the $r=... line with this:

$r = $wpdb->get_results( $wpdb->prepare( "
    SELECT SUM(pm.meta_value) FROM {$wpdb->postmeta} pm
    LEFT JOIN {$wpdb->posts} p ON p.ID = pm.post_id
    WHERE pm.meta_key = '%s' 
    AND p.post_status="%s" 
    AND p.post_type="%s"
  ", $key, $status, $type ) );

$r[0] should be your total. 🙂