This is a steamworks game so they will send you the key and you can activate it on Steam.
$89.99 USD on Steam.
This comes with the Professor Genki DLC.
This game has Single player and Co-op
Threadless have free shipping at the moment.
Normal shipping rates are approx (this is how much you'll save):
1-2 shirts are $9
3-5 shirts are $15
6-8 shirts are $21
Page 13 of latest Australia Post catalogue (top right corner). Considering current pricing of hard drives, $99 for an external 2TB name brand hard drive is pretty good.