Sorry, but I think you are trying to excuse the inexcusable. I have four eBooks published in the Amazon Kindle store and except for my own work and the Scrivener license, there were no costs involved.
In the past I also had printed works published and know the involved price difference.
Amazon revolutionized the publishing business -- they made it possible for all authors to get their work published on a global scale at almost zero cost. WITHOUT NEEDING TO GO THROUGH A PUBLISHING HOUSE.
So please pardon me when I call ******** on the argument that eBooks can even cost more than a printed version. I also say that it's ******** when somebody wants to make you believe that publishing an mp3 file costs more than publishing a CD, or that publishing an mp4 file costs more than shipping BluRay discs. It's like saying that the delivery of an eMail costs more than sending a hand-written letter. It's pure nonsense, plain and simple.
The truth is that publishing houses, record labels and disk manufacturers are quickly becoming obsolete and desperately try to uphold their no longer needed business models and services.
I can't argue about record labels, because they don't quite hold the same cards that the publishers still do. You can, for under $10k *buy* everything you need to record, edit, and publish your own music. And that assumes you don't already have a computer. For a couple grand, well within the range of a normal person to save up, you can buy a machine which will burn, *and print* CDs in bulk (1000+ to a run). Book publishers, on the other hand, are still largely useful because the primary way most people still buy books is from 'brick & mortar' book stores, and it's very difficult to get a self-published book into those channels.
Yes, e-books are starting to catch on, but it's still a small segment of the industry. High end printing and binding equipment is still impractically expensive for individuals (authors) to own, run and maintain. Print on demand has become marginally affordable, but it still eats a large share of the revenue (and therefore profits) involved in producing and distributing a paper book to stores. (I'm not entirely sure who you're referring to when you say 'disk manufacturers', so I can't comment on that either.
As for your contention that "there were no costs involved" in publishing your own e-book (beyond the Scrivener license). Great. I wish you all the luck in the world, but without advertising, you're unlikely to sell enough copies to pay for that license, much less actually live on. And if you didn't hire an editor, I can be quite confident that (despite your best efforts), your book isn't as good as you think it is. I'll concede that you may well be the exception that makes the rule, but virtually no one is capable of properly editing their own work simply because they're too familiar with it. Basic spelling and grammatical errors slip past authors simply because the author is subconsciously aware of what the text is *supposed* to say. Inconsistencies in the text commonly escape the author's notice for the same reason. Additionally, authors are notoriously bad at recognizing the sections of a work that are 'cool' in the author's, but serve no actual purpose in the story, leading to poor pacing and other issues. A good editing cycle includes someone who understands good structure, but is not intimately familiar with the work in question. They'll spot the errors, inconsistencies, and poorly written sections that the author will miss.
Additionally, sad though it may be, if your book doesn't have an interesting cover, most potential buyers are going to pass on it. If you didn't pay for the artwork on your e-book's 'cover', you're likely violating copyright, and that could cost you more than you could ever *hope* to earn from the book.
On the other hand, maybe you managed to actually get all of that for 'free', and you're running a grass-roots campaign to draw attention to your book instead of having someone else do it for you. Congratulations, you're not an author, you're an advertiser/agent/publisher/art director/etc. You're spending a bunch of time where you should be writing doing things that *prevent* you from writing.
Again, I wish you all the luck in the world. As an author, you'll need it. As an author who is actively ignoring the realities of the profession, you'll need it more than most.