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.
Honestly, there is a massive instructional benefit to being on a unified platform because it allows the cognitive load of the tool to get out of the way of the cognitive load of the work.
The problem is that TI has been pretty perfidious with their pricing and influence.
I hate to be that guy, but I think the only real solution would be to set up an open source foundation and create a unified standard for graphing calculator UI (including strictly defined key mapping/behavior) that would be applicable from Algebra up through Calc II. Then the market would be flooded with cheap chinese clones that can all run this firmware and cost like $15
Which is more than offset by the social cost of it being a monopolized proprietary platform. But since we have pretty good idea of what the requirements are for the common platform, it should be quite easy and, in the long term, a significant savings for a sufficiently large education body or coalition thereof to develop and maintain an open, unencumbered standard for meeting those requirements with a reasonable-cost certification program for those circumstances where certified-compliant implementations are important.