[imtringued]

Then you're back to $30 and can just buy an ESP32 with a screen module but suffer from the indeterministic USB stack. However you could also buy a $6 ESP32 and let it communicate with the smartphone over blue-tooth at a price point of $10 (phone) + $6 (ESP32).

[Jaruzel]

Agreed. There are many ways to skin this particular cat. It all depends on your use-case.