How to use automator to download only files from web directory that have changed since last week?

I wish to automate downloading an mp3 from a specific web directory (I have permission, and it is not password protected) each week, but only the single mp3 file that has changed since the previous week. I run a small LP/Internet radio station and we syndicate certain shows (with permission) and each one has its own unique way of getting files to their affiliates. This one show dumps their files into a web directory (http://www.ecoshock.net/affiliates/). I can easily write an Automator workflow that will Launch Safari, go to that directory and only download files that start with ES_ and end with _Affiliates.mp3, but I'd like to only download the most recently added mp3 that matches the criteria I mentioned. I assume it could be accomplished by adding a line or two of Applescript to the Automator workflow, but I do not know how to write Applescript.

Here's my current Automator workflow:

1) Launch Application - chooses Safari

2) Get Specified URLs - points to the directory I listed above

3) Get Link URLs from Webpages - Only return URLs in the same domain as the starting page

4) Filter URLs

ALL

Path contains mp3

Path contains ES_

Path contains _Affiliates

5) Download URLs

Right now this is to a folder on Desktop, but I eventually will have it add to iTunes and add some tags, create a Smart Playlist, and then close Safari.

I ***-u-me I can swap in a line of Applescript for step 4 above or add it right after, but I am open to other options.

Please help.

Thanks.

PS: If it was an anonymous FTP access I could also synchronize the directory using Transmit, but that isn't an option.