They cost so much because they're devices that are the only accepted model for school use. If someone made an equivalent and sold it for $50, TI wouldn't drop the price because the equivalent hadn't been certified as acceptable for test-taking.
Of course the whole thing is absurd. Algebraic solvers aside, being able to plug numbers into a calculator is all you'll be doing with one outside of very specific fields. Memorizing formulae is totally unnecessary, although knowing which one to use is important - and a calculator isn't going to solve that (Wikipedia or Google, on the other hand...)
I'm more surprised that there aren't decent graphic calculator apps for smartphones. I get the whole thing with physical buttons (and agree), but the last time I had to actually graph an equation I think I had to use excel or some janky web app because that's not in my day-to-day work so I don't have my old TI-83+ sitting around from high school.