Hard to set a price without knowing the details (screen size, UX, etc). Roughly, for a well reviewed product like this, I’d be willing to pay something in the iPad mini - iPad pro range.
Repurposing here would mean regular screen, i.e. not eink; I’m not interested in that.
Personally, I'd like to see more products that repurpose old phones and tablets while scratching that "new object" itch.