Bandwidth is precious, and seeing a bandwidth limit exceeded on your website is just so frustrating. Blocking unwanted referrers from your site may be your best option. If you are using apache as your webserver then you can take advantage of its mod_rewrite module to block unwanted referrers.
You need to modify your .htaccess file to block access to large files such as, images, mpeg, avi, etc. :
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://([-a-z0-9]+\.)?domain\.com [NC]
RewriteRule .*\.(jpg|gif|avi|wmv|mpg|mpeg)$ http://www.domain.com/nohotlink.jpg [R,NC,L]
</ifModule>
