I did a similar thing at a startup where I was working as a consultant. We would constantly run out of coffee cups so I started smuggling in more cups each day, some 50 in total. Luckily they were using cheap IKEA mugs so the total cost was roughly 100 €.

The problem could have been solved in many ways but it was a nice hobby for me. I ended up switching to work there as an employee and have been for ten years. I still use the mugs so it worked out OK.