Craigs list Responder

I am looking for a program that will allow me to search for a given set of keywords on craigs list. If the ad matches the keywords then an email should be sent to the reply-to address. I believe something like this already exists, but i cannot find it. I am willing to pay someone a commission for finding it for me. Otherwise i will accept bids for a custom app. If you are bidding for a custom app, it should be built in Java or PHP.