I agree - rsync would be a fantastic way to backup data files - and you can do so multiple times in a day without chewing up your bandwidth as it just grabs changes in files (though it might grab the whole file in a Windows system as opposed t oblock level changes in a Linux system). You would need to look into cygwin I believe.
Alternatively, you might also look up FileZilla Client (and lftp as Rog already mentioned), not sure how well it works through command line but I think it will let you synchronize and only get changed files.