If you’re heading off to university soon—or you have kids who are—you’re in for a shock. Textbooks now commonly sell for $150 each. Prices for these key books have been rising at twice the rate of inflation and the average student now shells out between $600 and $900 a year for them.

Luckily, there’s a new option: get your textbooks for free. Sites such as Textbook Revolution and Freeload Press offer free titles on topics ranging from algebra to psychology to earth science. You can download and print them yourself.

Jason Turgeon launched Textbook Revolution in 2004 in response to “greedy” publishers that he says are exploiting a captive market of students. “The problem is that it’s the professors who choose the books, but it’s the students who have to pay for them,” says Turgeon, a recent graduate from Northeastern University in Boston.

Turgeon says publishers have been using underhanded methods to pump up prices, especially in the science and business fields. They’re bundling textbooks with unnecessary CD-ROMs, producing deluxe hardcovers, and accelerating the new edition cycle in an effort to kill the used book market. “At first there were major changes between editions,” he says, “but now they often just change the font size and reorder the questions.”

Free textbooks vary in quality, just like for-profit books, but many are very good. Some were written by professors at Yale, Texas A&M and other top universities and donated to the public domain. Others were commissioned by Freeload Press, which makes its money from ads inserted into the books.

If your professor isn’t using a free textbook, Turgeon says you can still keep a lid on costs by using websites such as bigwords.com, abebooks.com and bookfinder.com to hunt down secondhand copies. But he says you should still bring the free texts to the attention of your professors. After all, if enough of them switch over, all textbooks could one day be free.