I'm making about fifty pounds a month from the two books' combined sales on Lulu - most of that from sales of ebooks, actually (I've been hampered by Lulu having poor ePub processing software, so I can't get the ePub of Sci-Ence! uploaded as yet, but am selling a surprising number of PDFs). I also got my books uploaded as Kindle books last month, and have made about fifty pounds so far from those (averaging one sale a day when I have them at $5, and three sales per day when I have them at $1).

So assuming sales stay more-or-less level that means I can average £50 per month per book without any kind of promotion other than my blog. However, I'm hoping that by increasing the number of books I have available (and by having them in niche markets - both my books have topped the Kindle charts for their respective categories, despite low sales) I'll get some kind of name recognition. It only needs one breakout success and I can make a significant amount of money. (There are people selling hundreds of thousands of self-published books a month, but they're primarily writing pseudo-Twilight 'dark fantasy', and I have too much sense of shame to do that ;) ).

I hope the Beach Boys one might be successful, especially since I have some name recognition within the BB-fan community (I was very active in online fandom in the late 90s and early 2000s).

(I slightly miswrote earlier, BTW - there is one career-retrospective look at the Beach Boys' music. Mine is significantly more in-depth.)