The University Book Center will shell out $15 for your used copy of ÿSabias que-?, the beginning level Spanish textbook. Or you could get $20 at the Maryland Book Exchange.

But one option some students are turning to is posting books and other media on trading websites. In return, students receive credits to purchase items others have listed. Abandoning the cash-based system that underpins other used goods sites like Craigslist and eBay, these sites are taking the Internet back to bartering.

Swapsimple.com, which pays in credits rather than cash, will give you 73 credits for that Spanish book. Higher dollar values mean more point values, a portion of which can be traded for books, DVDs or video games.

“I like that it’s trading rather than selling,” said Danielle Drecker, a first-year social work student at University of Maryland, Baltimore County, who posted a used GRE prep book last week. She didn’t expect to get much money from a bookstore, but knew there was demand for the book.

Swapsimple users post items and receive credits to buy other goods. The number of trades conducted on Swapsimple has climbed from one per week during its January launch to hundreds, said Elle Rengarajan, a company spokeswoman.

Swapsimple is one of many sites that facilitates trading of used books and DVDs that have recently popped up, with Zunafish.com, Bookswap.com and Campusbookswap.com among them. The sites employ a number of strategies for ensuring revenue, including advertisements and monthly fees, but not everyone is sold on the business model.

“I don’t see what the competitive value is in the long run,” said David A. Kirsch, an assistant professor of management and entrepreneurship.

Kirsch said he doesn’t see trading sites going out of business, but doesn’t expect big profits in their future, either.

Those prospects, however, don’t seem to worry Zunafish co-founder Billy Bloom.

“On Zunafish, there’s no profit motive whatsoever,” he said. “It’s all about the sharing of our communal materials with one another.”

Bloom said the idea for Zunafish came from an article about a DVD sharing website his business partner Dan Elias read.

“It got us thinking about the fact that we have all these media materials sitting around in our homes,” he said.

Until now, Zunafish, which was named one of Time Magazine’s 50 coolest websites, has stuck to DVDs, paperbacks, video games and CDs, but it plans to add textbooks in the next few months.

Bloom says the traffic on Zunafish has soared since it launched in January.

Though Zunafish and Swapsimple are relative newcomers, the idea of trading books is at least a few years older.

Campus Book Swap began in 2004 as part of the non-profit MakeTextbooksAffordable.com, a campaign launched by students at the University of California at Irvine to provide an affordable alternative to expensive textbooks.

“Our main priority is to point out the methods that publishing companies are using to artificially inflate textbook prices,” campaign coordinator Sabrina Case said.

Contact reporter Andrew Vanacore at vanacoredbk@gmail.com.