Publishing scholarly books and articles directly online is one of the great innovations of the digital age. There are some scamsters out there, however, who take advantage in particular of young researchers under pressure to publish.
The most recent Chronicle of Higher Education (9 March, page A6) discusses the strategy employed by one company who contacted a young researcher inviting a journal article submission, and then sent her a bill for $1800. She refused to pay, but the article was published regardless without any apparent editing, reviewing or the slightest correcting. If you don’t have a subscription, you can go direct to Jeffrey Beall’s Scholarly Open Access blog where he lists publishers to avoid.