Thomas Jefferson said that “books constitute capital.”

A Government Accountability Office report found that in the past two decades, college textbook prices have increased at twice the rate of inflation. During 2003-04, students and their families spent more than $6 billion on new and used textbooks.

According to the GAO, the average estimated cost of books and supplies for a first-time, full-time student in 2003-04 was $898 at four-year public institutions. That amounted to about 26 percent of the cost of tuition and fees.

That, folks, is not chump change when you consider that many students already are borrowing heavily to attend college. It’s not unusual for one textbook to cost more than $100.

But there are some things students can do now to reduce the capital they spend.

For instance, the California Public Interest Research Group (CALPIRG) recommends buying online at such sites as www.campusbookswap.com, which allows students to buy and sell used books directly from each other. The site is free but registration is required.

Try these sites as well: www.textbookx.com, www.half.com and www.bigwords.com. But be sure to factor in shipping expenses.

Before you buy, double-check that you have the correct 10-digit International Standard Book Number, or ISBN – it’s above the bar code on the textbook’s back cover or title page. If you are checking your class syllabus online, it should contain the ISBN along with the book title, author and edition.

If you’re really bold and struggling financially, there may be a way to use an old edition of a textbook. However, it’ll take some work.

First, check with the professor to see if the new edition of the textbook he or she is using for the course has substantial changes. If there aren’t many changes then look online (or ask the faculty member) for an old syllabus.

Why? Because a new edition of the textbook often means new page numbers and that in turn means the professor has to create a new syllabus. But if you can get your hands on an old syllabus with the old page numbers, you may be able to get away with using a previous edition of the book and save some money.

Used textbooks typically are priced at 75 percent of the retail price of the new book. Prices on used books range from $10 to $80, with the average price being about $40, according to the National Association of College Stores.

Most important before heading back to school, find out what books you have to buy. Many college bookstores post the required textbooks online for each course. You need to shop early so you’ll have a chance to buy used books, which often sell out fast once classes start.