Sure it's not a huge discount, but the DLC just came out 2 days ago, so it's the best you'll get for a while.
While it's been called a bit short, that can be said of most DLCs, but if you want more of Knifey, here's your chance.
Downloadable Content. This content requires High On Life on the same platform in order to play.
Does it have Roiland do the voice? I heard he's a bit of a scumbag. I bet he still profits from the game just as much either way, minus a voice acting fee.