Is there a command to get the download size (and maybe even installed size) of the total available updates? Update manager shows dl size, so that should also be possible via commandline, shouldn't it?
If there is not a straightforward command then maybe with python it can be retrieved. In /usr/lib/python2.6/dist-packages/apt/cache.py there are definitions that could be useful (requiredDownload and additionalRequiredSpace, lines 141-152). I have no idea though how to turn that knowledge into a python script that prints dl size for current available updates list (python /usr/lib/update-notifier/apt_check.py --print-packages).
Help is appreciated.