I dont quite understand your script.
However, from your 'artists/airgate/airgate.php' part, it seems that each artist listed has a directory and a page.
At the same time, 'artists_home.php' is the list of artists which is included in artists.php?page=artists.
In that case, maybe use:
<?php
if (isset($_GET['page'])) {
switch($_GET['page']) {
case 'artists':
include 'artists_home.php';
break;
default:
include 'cgi-bin/404.php';
}
} elseif(isset($_GET['artist'])) {
switch($_GET['artist']) {
case 'airgate':
include 'artists/airgate/airgate.php';
break;
default:
include 'cgi-bin/404.php';
}
} else {
include 'cgi-bin/404.php';
}
?>
A possibly simpler code might change the switch statement for the artists into:
if (file_exists('artists/' . $_GET['artist'] . '/' . $_GET['artist'] . '.php')) {
include 'artists/' . $_GET['artist'] . '/' . $_GET['artist'] . '.php';
} else {
include 'cgi-bin/404.php';
}