Threadless often have sales and this one is great for free intl shipping. Confirmed the code CYBERMONDAY14 brings intl shipping down to $0.
I added 5 x $5 plain t-shirts to my cart, $25USD free shipping with code applied. Thats 5 shirts for $30 AUD
As a long time threadless buyer I can add that the shirt quality is excellent, very soft and comfy and lasts well.
EDIT: Cart Picture: http://i.imgur.com/3uRo7mS.jpg
Unless they've changed their methods in the last year or so, then the shirt quality really varies from shirt to shirt. I don't know how to explain it but some shirts look and feel like they can go through a war, but some of the shirts have fallen apart after a one or two rounds in the washing machine.
Still, <$15, can't complain.