A start-up idea... A calculator app which can be configured to only perform certain, allowed operations. Teachers could announce that the next test would only

A start-up idea... A calculator app which can be configured to only perform certain, allowed operations. Teachers could announce that the next test would only allow a particular calculator configuration, and students could run the calc app on their phones/laptops with those restrictions (or none if they didn't want to prepare well for the test). Then, at test time, the teacher passes out purpose built "calculators" running the calc app as configured by the teacher for that test. The calculator would be free, but the teacher kit would be sold to schools. What would be the hardware cost in bulk for a cheap device that could run one TI calculator-like app? If students today can be required to buy a $100 TI calculator, could they be required to buy a flash-able "calculator" device?