Hey, everyone, I wanted to quickly let you know the game is part of the Humble Spring Sale here.
I didn't know that the Humble Spring Sale was coming when I put the game on a Weeklong Deal here last month, and unfortunately there is a two-month waiting period for sales here on Steam. This means that I'm prevented from reflecting the same 50% discount here on Steam. :-/
That said, Humble sales do come with a Steam key, so you can buy it there and then activate your game on Steam via your Humble account.
Sorry for the confusion, but I hope you enjoy the deal!