I wish I had a Curta II but those go for 600 dollars.
The mechanical calculator would need some display of small pin lights behind a perforated black piece of paper. That would not be oldschool demo coding it would be ancient demo coding. I hope to get by Adiator today the abacus is coming from japan so I plan to make my own in the mean time. I had to go to a pink painted ladies' craft store for the little wooden beads. It was really humbling and terrifying. I can provide project plans if anyone is interested, I drew some up on AutoCAD.
The plans are in inches because I reject the rest of the world's measurement system.