I just got back from the post office.  I walked 
in, grabbed the entire stack of priority shipping 
cardboard they had left (about 13 @_@) and left 
really really fast ^^ hehehe... I think everyone 
behind me waiting in line to use those things were 
a little peeved, but oh well :)
They're sturdy enough to make for good packaging, 
sized nearly to perfection, and I can just fold 
them inside out to send internationally.  Perfect 
alternative to "cutting up pizza boxes" ^^
Thanks for all the suggestions everyone!
-Eric