Consider - an app that replicates this functionality on the phone, but tracks if the user at any point closes the app. This then is reported to the teacher so the teacher knows if there was any cheating.
how about: a standardized test calculator specification, with careful boundaries around what is required, what is permitted and what is not.
Then let competition drive prices and features.
And in-car driving instruction happens with the teacher next to the student in a car they're familiar with. It's not like they're radioing to 30 students each in a separate car.
Also, the calculator is a tool to teach math. If someone gets distracted figuring out the calculator, they're behind. The student driver car is to teach driving.