By Kirsti Knolle and Georgina Prodhan

FRANKFURT (Reuters) - For any author frustrated by rejections from publishing houses or wanting to cut out the middle man, there has never been an easier or cheaper time to self-publish.

A host of free self-publishing platforms offered by Amazon, Apple and specialists like Smashwords have created new opportunities and a huge market for both unknown hopefuls and a few established writers.

Hailed as democratizing the market by some and decried as cheapening literary culture by others, self-publishing has transformed what it means to be an author. Simply uploading a PDF file and making a small outlay for cover design can turn anyone into a published writer on an ebook platform like Amazon's Kindle, earning up to 70 percent of the cover price.

The traditional role of the publishing house - sifting through manuscripts, editing those selected and packaging, marketing and distributing the finished book - is eliminated. The publishers aren't too worried, though. Self-publishing can work to their advantage, too.

E.L. James is an example. Her "Fifty Shades of Grey" was self-published. Then it was picked up by Random House and became the fastest-selling paperback of all time, propelling James to the top of the Forbes list of highest-earning authors in 2013.

Few self-published writers will see that kind of success. But those who actively promote their own work and price their titles keenly enough - sometimes as little as 99 cents a copy - can break through to a mass audience.

"A lot of self-published books, while they're not up to the standard that established publishers would want, are good enough," said Edward Nawotka, editor-in-chief of online magazine Publishing Perspectives.

"They are priced at a point that meet the reader's demand," he told Reuters during the Frankfurt Book Fair. "I think it's expanded the market for books."

STIGMA

Almost half a million titles were self-published last year in the United States alone, an increase of 17 percent year-on- year and 400 percent since 2008, bibliographic information firm Bowker wrote in a report last week.

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The global market is still largely uncharted.

"Self-publishing is beginning to mature ... It is evolving from a frantic, wild-West style space to a more serious business," wrote Beat Barblan, who heads the Bowker department that hands out unique identifier numbers for books, or ISBNs.

Mark Coker, who founded Smashwords after having his own co-authored novel rejected by publishers and now helps almost 100,000 authors, wrote in a recent blog post: "The stigma that once haunted self-published authors is quickly melting away."

Self-publishing has a long tradition. The world might never have read Charles Dickens's "A Christmas Carol", Mark Twain's "The Adventures of Huckleberry Finn" or James Joyce's "Ulysses" had the authors not taken matters into their own hands.

Still, many self-published authors publish only one book and reach a small audience.

Ingram, the world's biggest book distributor, says its average self-published title sells 100 copies in print or digital, and a 2012 survey by content marketing firm Taleist found half of self-published authors earned less than $500 per year.

To make a living takes incredible luck, or determination and hard-headed business sense, as German fantasy-fiction author Ina Koerner knows. She has sold more than 300,000 books via Amazon under her pen name, Marah Woolf.

"You have to deliver a book every half year, otherwise you will be forgotten," the 42-year-old mother of three told Reuters at the Frankfurt Book Fair, the world's biggest book trade gathering. "I write for a market and the book is a product."

Koerner, who trained as a banker and was rejected by 15 publishing houses before taking the decision to self-publish, logs onto her Facebook account daily to keep in touch with her 2,500 fans, and posts on her blog at least once a month.

"I have little understanding for authors who think they have written 'the' book but no one sees it," she said.

ADDITIVE, NOT CANNIBALISTIC

Success also takes a degree of humility and realism.

Koerner prices her books at 2.99 euros ($3.79). She earns 2 euros for herself; Amazon takes the remaining 99 cents.

Penelope Ward's self-published teen romance "Stepbrother Dearest", which debuted at number 2 on the ebook bestsellers list last week, was priced at $2.99, compared with an average price of $7.74 for the top 25 titles.

The popularity of this kind of genre fiction has contributed to the decline of imprints such as Harlequin or Mills and Boon. But it has had minimal impact on the rest of the industry, which could barely cover its costs at the prices typically charged.

"We believe the rapid rise of self-publishing is more additive than cannibalistic, and will generate a few, but only a few, hits," analyst Douglas McCabe of Enders Analysis wrote.

(Corrects spelling of writer's pen name in 16th paragraph.)

(Reporting by Georgina Prodhan; Editing by Michael Roddy and Larry King)