Not that that takes away from the article at all. This project has many merits, and although cost may not be one of them, it’s still interesting!
Are far as low volume prototyping goes, sheet metal is as cost efficient as it gets for large metal parts. If you're sourcing from China, I'd estimate 500 bucks per prototype (with two sets in case one breaks).
I love the visual interface of your version.
There’s also a few things I love about an adjacent app (https://www.lifecalendar.io/) and I have a few feature requests for the back burner:
1. I love the idea of seeing my entire life in one structured grid. We lose the playfulness of your version. But it is a harrowing reminder of how much time is left. Would it be possible to implement such a view?
2. Filter/views for events types (vacations, career, etc) to change the perspective on specific topics.
3. Empty headlines permitted. This would allow me to use this as a low resolution weekly journal, that shows the entries only on hover. If we want to warn users of actual empty headline mistakes, then we can substitute with a special character or the like.