The DLC would be around $3 after the campaign is over and released. The artbook around $5 (pdf). Any pledgers in this campaign of $3+ will receive the DLC (if the any goal has been met).
Pledgers of $5 and above will receive both DLC & Artbook via e-mail (DLC only if any goal has been met).
Since the goal of an artbook is reached, it is in development. I started planning the DLC, but will start working once a goal has been reached. I'm sorry for the confusion. Hopefully, this will clarify it! (Edited in all posts)
I noticed some donations via itch, so these will count towards the endgoal too.