I am looking for a robust FTP transfer script that I can use with cron, any recommendations?
I would love a script in Python that could run in the background.
cURL is another option: it can do more, but is proportionately more complex too.
You'll find all the above in the standard repositories of just about any Linux distribution.
What tool is best, of these or the many other that are no doubt out there, depends on what your more exact needs are.
I used to use the ncftp suite, which included ncftpget and ncftpput. Still do, if I can get my old .SRPM to build (which is becoming an increasing rarity). Sadly, they seem to have fallen out of favor in the distributions I use.