Amazon subscriptions add to e-book deals

Amazon Kindle e-books book publishing
Will Ireland | Future Publishing | Getty Images

E-books aren't exactly bound for the bargain bin, but avid readers may find a few other ways to build their digital library with less cost.

Prices of e-books have been dropping since last fall, when the Department of Justice achieved settlements with major publishers over price-fixing allegations. As a result of new agreements that allow retailers such as and Barnes & Noble more pricing freedom, the average price of a best-seller was $11.79 in October; by late August, it was $6.33, according to Digital Book World, an industry group. On Friday, the DOJ issued an order requiring Apple to modify its agreements with publishers in a similar fashion.

Booksellers are now experimenting with even lower-priced and free reads. Next month, Amazon will launch a service, MatchBook, allowing customers who have purchased select print books through the site to get the e-book version for $2.99 or less. Some titles will be free.

Start-ups such as Oyster and eReatah have taken a different approach with subscriptions. Oyster offers all-you-can-read access for $9.95 a month, while eReatah's plans start at $16.99 for two titles.

(Read more: Simple steps to avoid growing bank fees)

The e-book market is maturing. Over the past five years, sales have grown 76.2 percent a year, said Jesse Chiang, an industry analyst for IBISWorld. Now that many of the people who want to read digitally have made the switch, annual growth over the next five years is expected to be closer to 7.5 percent.

At first glance, the new offerings are a better bang for your buck that buying titles individually, said Peter Hildick-Smith, president of research firm Codex-Group. For example, a consumer might buy a print book as a gift in Amazon's program and keep the e-book, or use an added e-book to leave a weightier tome at home. And with some new e-books still retailing above $10, multibook subscriptions could help readers cut their book bill.

But the new programs' big hurdle is selection. Publishers will need to be onboard with the e-commerce sites to have their titles included in bundles or subscriptions. Even then, many titles aren't offered as e-books, Hildick-Smith said. So, depending on their tastes, even voracious readers may find that they can't take full advantage of the programs.

Oyster has 100,000 titles and eReatah 80,000, while Amazon's MatchBook will start with 10,000. (For comparison, just the "Action & Adventure" niche in the fiction section of the Amazon Kindle Store comprises 57,041 titles.)

"That's definitely a limiting factor," said Chiang, though the sites have all said they expect the number of available titles to grow quickly.

(Read more: Apple's planned trade-in program: Should you bite?)

Consumers should also consider their reading habits before buying a subscription. "Subscriptions services assume people are going to consume book content steadily," said Michael Norris, senior analyst for Simba Information. But most adults pick up a book intermittently, which could reduce the value of a subscription for several books a month, he said.

Readers may find that their local library is an even better option for free books than in the past. More public libraries have been developing e-book content management systems, negotiating with small publishing houses and self-published authors to offer materials at lower cost.

While a digital copy of a best-seller might cost the library $85, for instance, small publishers may charge $4, said Jamie LaRue, library director in Douglas County, Colo., which launched its own system a year ago.

(Read more: Retailers entice shoppers with elite loyalty perks)

It now offers 40,000 titles, including 10,000 self-published ones.

"It started slow, but we now find that we're checking out 300,000 titles a year," LaRue said. Libraries in states including California, Massachusetts, Florida and Texas are following suit.

By CNBC's Kelli B. Grant. Follow her on Twitter @KelliGrant.