That's a part of what the article dives into. For example the LED matrix hat they were using from Adafruit was probably the most expensive option they could have used at $25/unit, and the article gave examples of much cheaper (i.e. 10% of the cost) parts that would have done the exact same job with a little extra engineering time/effort. Replacing the Pi with an ESP32 would have saved money, but like the article mentions using a Pi wasn't entirely a bad idea considering the free marketing they got from the foundation.
