I aim for quantity over quality. I pay to have books ghostwritten for a particular market/niche. I also acquire rights to other self published books and re-release them. Self publishing is all about the marketing.
For ghostwriting I focus on a couple different niches. I work with a company to get the books written. I write for the audience rather than what interests me. If vampires are hot one month I put that out. If it's billionaires the next I do those. I have a couple different "authors" that I write under that stick to each genre (One only writes LGBT Romances for instance). A large part was building up the email lists of readers and managing some social network profiles. Once you build up your following it gets much easier. I know some authors that churn out a book every 2 weeks and people will spend the $2.99 (or read it on kindle unlimited) every time. My release schedule is a lot slower, but I'm trying to find more reliable ghostwriters to speed it up.
Regarding the buying of book rights. I have a publishing company I run that looks for books that are not 'successful' and I make an offer. I'll clean up the book and re-release it under a different author name and do a little marketing. These I aim to cover costs before end of the first year.
Usually it costs me around $1000 for a ghost written book. Book is around 35k words (3c/word). Editing is 1.5c/word or flat rate depending who I get to do it. Covers are usually $250 for ebook or double if I get physical.
I use vellum to format ($250 one time). Requires a mac. The company I use will sometimes do this for me for free.
Marketing beyond email list is then either book bub if I can get in or amazon ads.
Mailchimp/digitalocean for email list/Wordpress site hosting. Google Apps for email. Those are my reoccurring costs.
Break even is usually 800-1k copies sold @ $2.99 list (I earn 70% of that). Plus whatever I spent on marketing. Anything outside 2.99-9.99 Amazon will only pay 30% royalties. I earn roughly a dollar per book read via kindle unlimited.
The first few books will take a while to earn back. Building your following/email list is the most important thing. I use it for engagement. “New book coming soon! Giving away 25 advance reader copies enter here”. Then before release “pre order now. Here is the feedback from those that won a free copy.” The surge of reviews/early sales helps boost Amazon ranking (new readers) as well as to quickly earn back what I spent producing it.
100% Amazon. Kindle unlimited locks you in. But, worth it for what I publish. Physical/print on demand book margins are pretty bad. I have some physical books. But most are ebook. All of my bought/rereleased are ebook.
About $3-4 a year. Usually around this time of year when people are buying gag books. The first slew of sales actually came from amazon book reselling bots buying it. Guess they never figured out that it was print on demand.
I aim for quantity over quality. I pay to have books ghostwritten for a particular market/niche. I also acquire rights to other self published books and re-release them. Self publishing is all about the marketing.