I use podget, which is a 248 kB bash script. I really like it, and think it will meet your requirements:

• It’s designed to be called from cron
• It lets you sort your podcasts into categories
• It automatically organises the downloads into different directories based on these categories

From its description:

Podget is a simple podcast aggregator optimized for running as a scheduled background job (i.e. cron). It features support for downloading podcasts from RSS & ATOM XML feeds, for sorting the files into folders & categories, for importing URLs from iTunes PCAST files & OPML lists automatic M3U & ASX playlist creation, and automatic cleanup of old files.

It also features automatic UTF-16 conversion for podcasts hosted on MS Windows servers.

Run podget once to install the users configuration files to $HOME/.podget, and then customize them there.