Typically, the price of books is largely a function of the costs of manufacture and distribution. There are some fixed, up-front costs that don't vary with print run (editorial, typesetting, proofreading, cropyediting and so on), which is why a bestseller novel is way more profitable than a complex academic book that is expensive to produce and limited in sales, even though you're probably spending more on royalties and marketing support for that.

For ebooks, you can reduce your distribution costs (there's some cost of creating the file and distributing it, but you don't have shipping costs or returns), but of course you still need to make back your fixed costs. I manage ebook production for a university publisher (but I have no say on pricing decisions, only the technical stuff), and for us, the savings for ebooks doesn't really translate into a big price difference, because our fixed costs are such a large part of our expenses. In our market, ebooks still don't amount to a big percentage of sales, because the reader technology doesn't provide enough support for complex books.

I do argue as much as I can against DRM, but so far I have lost that fight.