I went and looked at my copy of Rifle Accuracy Facts, and apparently the copyright is held by Precision Shooting, not Vaughn & his heirs. The book contract though, may have given Vaughn certain rights vis-a-vis any electronic editions, so I don't know the whole picture.
I will say that if I had the text on disk, and the images, I could put together a nice ebook in PDF format.* As I'd donate my time, and as there are no printing costs with an ebook, aside from any distribution costs, there would be no cost for the entire project.
If downloading the book could be hosted by a site (like BR Central) for free, the entire book would incur no costs. Any price then, would be determined by how much the copyright owner and author wanted for the book.
Getting books to "camera ready copy" is what I've done for over 30 years. Easy enough to do, though as I'm semi-retired, it would take a while. Particularly to straighten out those images.
Charles
*There are advantages to pdf over ePUB, even with the as-yet-to-be-tried ePUB3 spec. Far as I'm concerned, EPUB is just a way the device manufacturers have come up with as a way to push their products over other manufacturers, and I won't do that kind of work. The same with Digital Rights Management. Most follow up studies concerning DRM shows it hurts a publisher's profitability, but it is pushed by the reading device manufacturers.