In case anyone finds this thread via search, I just found this website:
http://www.iwebtool.com/speed_test
It tests the speed of the loading of your website, but it also tells you the size of the page. So, just type in a wordpress blog that’s similar to the one you’re setting up and multiply the size by the page views.
BTW, 2000 views of my current blog’s front page (6 pics including banner) results in 84,000 KB a day so more like just over 2 GB a month if my math is right.
