The ebooks are priced from deer nuts to $3.99. The revenue is split between the contributing writer, Amazon, and the licensee, beit an author, publisher, or mega-media conglomerate.
Amazon has also opened up the Kindle Worlds submission page today, and I strongly urge you to got take a look. While Amazon has conned some into thinking that any writer can submit a story, that page includes a long list of rules and requirements set down by Amazon and the licensees.
Authors are also going to have to give up a lot of control in exchange for the chance to possibly make some money. Here's a telling excerpt from a Q&A that the head of Kindle Worlds conducted with Barry Eisler, one of the KW licensees:
Our publishing agreement is an exclusive license to the story and its original elements for the term of copyright. Because of this, we recommend writers do not incorporate a character or new element into a Kindle Worlds story unless they want them an exclusive part of that World.
All these rules, restrictions, and demands on the part of Amazon render dubious any claim of a connection to the free-for-all that is fanfic.
Admittedly, some of the licensees are going to allow generally free reign in their Worlds, but Amazon's rules still exclude stories. I would say that it is now pretty clear that Kindle Worlds is not a fanfic free-for-all, but a licensing program for sanctioned stories.