But many students say the cost ultimately didn't faze them.

"It was definitely a big factor," Keon says. "But when you think how expensive medical school is, it's kind of a pre-cost."

Kiprilov points out that most students spend thousands of dollars just on application fees, and thousand more flying to interviews across the country.

That willingness to spend contributes to "obscene" profit margins at most companies, says Ari R. Freiser, the founder of TestWell.

Freiser says a few large companies are able to pocket huge profits because they are industry leaders.

"With a thousand dollar price tag, commercial test prep is a way of saying to people who already have an advantage in society, 'this is a way to buy even more of an advantage,' and to those who can't, 'take a hike,'" he says.

But representatives of Kaplan and Princeton Review, the two largest test prep companies, point to their scholarship programs, which provide discounts for students who cannot afford full price.