According to Publishing Perspectives ISBNs cost £89 (US$117) singly or £149 (US$196) for 10. No wonder lots of self-published books dispense with them. Now that you can get them on-line in UK as well as in USA, one wonders why they have to cost so much.
This chart comes from a report by Bowker trumpeting the increase in indie publishing. (Click on it a couple of times, and it should enlarge adequately. Or just follow the link to the Bowker report.) But of course it doesn’t tell anything like the full story as it is just a report on ISBNs issued — which is what Bowker does. Almost 80% of these ISBNs are for print books with Amazon’s own CreateSpace as the consumer of almost three quarters of those. One can see how having an ISBN on a print book might be a good idea — otherwise it’s going to be hard to get it into established distribution channels — but an e-book can thrive without such help. There seems to be no real way to measure the true extent of the self-published e-universe, but we can rely on its being more than 153,160 titles in 2015.
Of course we have to acknowledge that nevertheless, almost three quarters of a million self-published ISBNs represents a huge number of books. I despair of finding what the real number of self-published books might be.
For those who may want to know how an ISBN is constructed, and what its various bits signify, my post Bookland EAN & ISBNs may be helpful.