It depends. Most seem to hover in the neighborhood of around $.01 – .02 per word; take someone like this guy, who I've thought about hiring: http://www.mikesirota.com/fees.htm . A typical novel will run about 85,000 words, so he'll probably charge about $1500. I think these guys: http://www.bookdocs.com/ charge similar prices. If you want to publish a 250,000-word epic fantasy novel, that's obviously going to cost more.
What does it cost for an editor to edit a 300-400 page novel written by a decent author?
How about cover art?
Marketing is an entirely different animal. I dont think you do book tours for ebooks.