While sky-high U.S. college tuition might be the headline number, here is a sneaky little figure that might surprise you: the cost of textbooks. "Atrocious," said Kashif Ahmed, a financial planner in Bedford, Mass. — and himself a college professor for more than 20 years.

In fact, estimated student budgets for course materials are around $1,240 annually at four-year colleges, according to the College Board.

During the last four decades, the price of college textbooks has risen faster than any other element of the Consumer Price Index, according to Richard Baraniuk, founder of OpenStax, a nonprofit provider of free educational materials.

For the many students who subsist on ramen noodles and search couch cushions for loose change to last the semester financially, that is a punishing figure.

Now, the good news:

Textbook prices are edging back down, according to surveys by online booksellers CampusBooks.com.

For that you can thank a mix of factors, like the shift to digital copies; a more vibrant marketplace of online sellers; increasing prevalence of book "rentals"; decreasing college enrollment; and a broader push toward free materials.

Those macro publishing trends, combined with a little old-fashioned student creativity — like accessing library copies or sharing materials with study buddies — mean that you can slash textbook costs.

Here are four cost-cutting tips from the experts:

Rent textbooks

In the old days, pretty much your only options were buying and selling.

Nowadays you can actually rent copies, at sites like Amazon and Chegg.com — paying a more affordable fee, while establishing a fixed return date.

According to the National Association of College Stores, 45% of college students now say they rent textbooks.

CampusBooks.com offers a Buy vs. Rent algorithm, using data science to predict what future buyback figures will be, so you can decide on the right option.

Go used — or digital

There is often no reason to buy a brand-spanking new physical copy of a textbook. As a result, 56% of students buy used copies and 25% buy digital, according to the National Association of College Stores.

Ask the professor for the book's ISBN number to ensure you are getting the right edition.

However, since publishers do not receive a cut of used sales, they are getting crafty and providing additional chapters and updated content through one-time-only codes, notes Alex Neal, president and founder of CampusBooks.com.

If you need access to that, you may need to buy a new book.

Think about timing

Who tends to get snookered on high textbook costs? The wide-eyed freshman who shows up for the first day of class, heads immediately to the campus bookstore and buys a brand-new copy.

Upperclassmen tend to be much savvier, Neal said. By the time students are seniors, most of their book buying is done online, where they can comparison-shop and secure the better price.

Also, just like any other market — do not buy when others are buying, or sell when others are selling. That means obtaining a copy early, if the course syllabus is available.

And instead of selling in December or May, right at the end of the semester when everyone else is dumping their books — wait until January or August, when your copy will probably be more valuable.

Take advantage of free materials

As a response to out-of-control textbook costs, Baraniuk set up OpenStax to create their own high-quality textbooks — free online as well as print copies basically at cost.

OpenStax has issued 38 textbooks, used in 58% of all colleges nationwide, with 2.7 million students studying their materials in the last school year.

Since inception, that has saved students about $600 million in total.

But it is a moot point if your professor is not using OpenStax as the course textbook. So compare your options — it might be that one course is not using OpenStax, but another comparable one is, Baraniuk said.

Students would also be wise to lobby their professors to adopt free materials — not only to lower their own costs, but those of future students as well.

Said Baraniuk: "Too many students are having to make a choice between buying books and buying groceries."

Chris Taylor writes for Reuters.