At a writers' conference years ago, I had the unexpected pleasure of spotting someone reading one of my books. I was sitting across from her, and couldn't help smiling to myself--it was the first time I'd spotted a reader "in the wild." When she looked up and recognized me, she waved the book, calling, "Oh my gosh! I just bought your book!"
I thanked her and signed her copy, but when I tell this story at conferences, I tell the audience that I was tempted to say, "Oh my gosh! That's great--I just bought a Snickers!"
Why? Because despite her paying $14.95 (plus tax) for my book, what I would eventually see in royalties for that one sale was about enough for a Snickers bar (albeit a king-sized one).
As a book author, you can't count on royalties anyway--the majority of traditionally published titles fail to "earn out," or pay royalties. So when you write a book, you should write it for the advance--and look at royalties as something you hope for and aspire to, not something you count on.
That being said, half of my books have earned out and pay royalties. Here's the breakdown on one title--the trade paperback retails for $14.95, with a royalty percentage of 7.5 percent. That translates to $1.12/book. However, the e-book version pays a royalty of 50% of the sale price (about $7.76/book), which translates into $3.88. Even though the e-book is cheaper for the reader, the latter produces a royalty that's more than 300% higher than the print version.
The lesson? As a book author, I promote my books all the time. But I'm going to promote the e-versions of my books over the print ones. It's a better deal for my readers--and a better deal for me.