It really also depends on what is installed. for example if you use xfce instead of kde you will far less often get updates for your de 
same applies to other software. if you choose the sort of software that ist pretty heavy in Development you will get more new file from them.
my updates are sometime like 2gb a month, sometimes more like 1gb. it depends also on how much packages you have installed of course
if you try to stay minimalistic as possible for your need you may also safe some mb of updates.