I recently bought a plugin from GT that is an expirator. We paid just a bit extra to have them customize it so I can turn it on/off for individual links. It is working great! It will email the link owner and the admin based on criteria you set (like 1 week before link expires, upon expiration) it will purge expired links (if you wish). It is a bit pricier than I think you are talking about... but I thought I'd let you all know. It's a Classifieds plugin.

Take care,
Evoir