Question: I'm currently in a country where internet access is expensive (New Zealand), and I'm curious if I'll be able to download Portal 2. How big is the download in Steam?

Answer: 
The [system requirements](http://store.steampowered.com/app/620/) list 7.6 GB for Portal 2. If you already have a Source game the size could be much smaller since the Source engine compromises a large part of the download.
Yeah like all the other have said, Need to have Source SDK Base 2007 installed already, and that file is a whooping 4.8Gigs (if i remember correctly - around 4gig range) So I would say Portal 2 is roughly 2.5 gigs