Ebook pricing is broken. Sell it for $0.99 and you'll get buyers. You can't sell ebooks when it costs only 5-10% less than a dead-tree hardcover variant. People don't like being ripped off.
Books are far cheaper to print than most people realize. If you see a publisher charging 5-10% less for an ebook than a physical book, it's because they're pricing the ebook at whatever the physical book's price is, minus the printing costs.
Before ebooks came abundant the publishers said some 10% of book price is their money, another 10-15% is for author and editors, and the rest is eaten up by print and distribution+shop. I guess the distribution through publishers' site can be done at 20% of sales price.
The major costs you're missing are marketing and "plate" (up front cost to produce the content). Those make up most of the total costs. For textbooks, the decision makers are professors (so door-to-door sales to get their attention), and the market is pretty small, especially for upper level content (so few units to amortize fixed costs over). Print, paper, and binding are cheap, say ~$10-12 average for a textbook. Typically, distribution channel takes a 20-25%, depending on channel partner, and many colleges mandate that sales go through the school bookstore because they get a cut, so publisher's website isn't necessarily a viable option (without a lot of student marketing). Author royalties run ~13-15% of revenue, and editors hit plate expense (they're publisher employees, so not a variable cost like authors). Textbook publisher Ebitda margins wind up running 20-25%, but most publisher's pay a lot of interest expense, partly because the major costs are up front, and partly because there's been a lot of PE ownership. Net margins can be tight as anyone else's.
Source: worked for a plaintiff publisher in this case. Think Pearson, Cengage, and MHE all publish financials also.
There's a fairly small pool of readers for a niche technical book. Selling it for $0.99 won't meaningfully increase the number of buyers, and it won't recover enough revenue to meet the cost of production.
