Statista (The Statistics Portal) looks like it has some relevant ebooks revenue information (though not exactly what you are looking for). Unfortunately, you are forced to sign up for a premium account to access most of the reports. A sample report that they actually show you some of the information for is here (Global e-book revenue from 2009 to 2016*, by region (in million U.S. dollars)
, obviously some is projection).
I did manage to find an informal survey done by Marie Force about independent publishers here (covers total unit sales broken down between 2010, 2011, 2012 and some of 2013) . Here is an excerpt:
The conversation on the loop led to me post an informal survey to get
an idea of how our members and their self-publishing friends are
really doing. I didn't ask people to give dollar amounts, but rather
just their number of sales in 2010, 2011, 2012 and so far in 2013. I
asked them to list their most successful book in 2012 and how many
copies it sold. At the outset, I want to say that this survey was
informal. There is nothing scientific about it, but it does provide an
interesting snapshot of how self-published authors are really doing.
To give context to the numbers, I wanted to also provide a guide to
what the most popular price points translate to in actual dollars.
Using Amazon's conversion chart, here it is:
0.99 (35 percent royalty): $0.35 per sale
1.99 (35 percent royalty): $0.70 per sale
2.99 (70 percent royalty): $2.04 per sale
3.99 (70 percent royalty): $2.74 per sale
4.99 (70 percent royalty): $3.44 per sale
While I didn't ask authors to list their most common price point
(which I will add to the survey next time), I thought the breakdown
above would be enlightening to the authors out there who might be
waffling about whether they ought to try their hand at
self-publishing. If you are thinking about whether or not you should
dip your toe into the revolutionary waters, ask yourself these
questions: When was the last time I made $3.44 on the sale of one
book? When was the last time I made even $2.04 on the sale of one
book?
She then goes on to post a bunch of survey results broken down by author. Here is a sample of one of the survey results:
Elisabeth Naughton
Romantic Suspense and Paranormal
Total number of
self-published titles: 12
Total number of self-published sales in
2010: 0
Total number of self-published sales in 2011: 0
Total number
of self-published sales in 2012: 102,179
Total number of
self-published sales so far in 2013: Jan-March 2013: 370,059
Most
successful book in 2012 and how many sold: MARKED - 30,673 copies
I've been traditionally published for four years and my income comes
primarily from my self-published titles, NOT my traditionally
published titles.