How much does it cost to hire someone to write a five chapter's book?
Answers: Its not clear to me in your give somebody the third degree if:
1. You're supplying the plot, storyline, etc. & asking
someone to write a story from that.
2. You're asking someone to re-write/edit a story
you've already written.
3. You're asking someone to write a story of their
own, from scratch, on any subject.
Whichever track you're asking, the charge is usually figured on a per word or per page font.
Having done some proofreading/editing, the cost per word can range from 3 to 6 cents & the cost per double-spaced page is around $6 USD. A lot depends on the topic.
A guesstimate, figure 20 double-spaced pages per chapter x $6 USD x 5 chapter would be $600.
Your best bet would probably be to go on the internet & go through for some websites that list fees for writers liable to work on projects; or post an ad on a college campus to see if you could carry a student to do the work.