D K I don't know what substantial means in this business, but I have made more than I did on my traditional audio publishing deal for Rooftop Diva. In November and December I moved an average of about 450 royalty paying books each month. Most of my sales are not erotica, but African American Urban fiction, which I wrote my first book in that sub-genre in May 2013. I still write and publish all types of work. Since May of 2013 I have written 6 books that I selected Erotic fiction as the classification when they were published and that's out of 35 titles. There are 2 nonfiction titles, 1 gay/lesbian title, 1 reincarnation and 1 nonfiction title.
My recent titles are aimed at what I think is an underserved market of erotica about folks aged 50 and above. Our population above 50 is booming and they live full lives, so why should they have to only read about the faboulous sex lives of twenty something year old people. Unlike what a certain youg pop star said(Miley Cyrus), people over forty still have sex.
I'm writing and pubishing an average of 4 books per month since May 2013. I don't know how long I can keep that pace up, but it gives readers more to read and buy with the genre variety with a total of 59 titles online now as of this message. My idea is I need to build another genre with reasonable sales volume and erotica is slowly growing.
Most of my books are priced at $2.99 and I increased the price of most of my books that stated at $.99 to $2.99 a coiple of months ago after reviewing the page counts and they still sold in the same quantity range by were earning over $2 per sale instead of $.35 per sale.