Which make me to check and... a TI-89 is still over $100.
If you want something newer with more power and more features they also have the Nspire line of calculators but the TI-89/TI-83 basically the staple calculator for highschool math.
That is exactly why it would rub people the wrong way on a site where people are interested in entrepreneurship and also in disruption. Being approved by standardized testing institutions becomes a barrier to entry and a means for rent seeking. Of course there could be far better calculators for lesser cost that aid learning better, and more clearly reflected the types of tools that should be the default quality for practitioners in the real world.
Compare the HP-12c in finance. It's extremely well-designed and optimized for a lot of patterns, and it even has a moderately steep learning curve that seems to enamor it to its users, yet it is absurd to argue that absent certification as an approved calculator for the CFA that there would not be be even better handheld calculators used more often that people spent time to learn.
The TIbcalculator doesn't address either demand that goals of high school mathematics should address. It doesn't expose students to the state of the art, and despite its constrained capability it is costly enough to shrink the talent pool of high school students who get to take the tests that show off their aptitude and achievement.
Why would calculators be needed for a calculus test?
I think the problem is far closer to the grassroots, down to individual teachers taking the easier well trodden road of TI monoculture for various reasons ranging from ignorance, busyness or fear.
They absolutely do have competition, see for example the HP Prime, which is far superior (IMHO) to any calculator TI puts out.
The issue is that TI has a very effective market lock-in, so they don't have any incentive to innovate. They know students in the US will still buy their calculators because they won't be allowed to take the test if they don't