Go take that class at Johns Hopkins, then click on this link: http://store.wolfram.com/view/app/mathforstudents - $139.95 for a fully functional student version. You can also get a semester version for $44.95.
"Note: Mathematica for Students is intended for students enrolled in accredited academic institutions and is for use on a student's own personal computer."
I suppose many don't. I guess it depends on the meaning of "too high" for a student. I took it to mean "students cannot afford to pay $139" rather than "at $139, students will prefer to get the software illegally, even though they could pay if they chose to".