here's some rewrite rules you can stick in an .htaccess file when your client doesn't pay their bills and you want to disable every page on entire site w/o deleting or moving anything:

RewriteEngine   On
RewriteCond     %{REQUEST_URI}  !^/payyourbills.html$
RewriteRule     .*              /payyourbills.html          [L]

just put the page you want everyone to see at /payyourbills.html, and every request for any page will go there. also, no one will see /payyourbills.html in their url, just the url they typed. if you want people to see it change the [L] to [R,L]