Sounds like a very ripe prospect you’ve got there. Very exciting.
First off, for anyone else in a situation like this (with a friend), or themself, I highly recommend checking out the The Ultimate Beginner meta-thread.
For your friend, at first thought, I’m inclined to recommend some Hoppe.
For praxeology foundations, Economic Science and the Austrian Method provides what you’re looking for. However, it’s less than 100 pages, so obviously you’re going to want more. That’s where A Theory of Socialism and Capitalism comes in. Read Mark Thornton’s article that is provided in the links section there for a great overview to see if it’s the kind of text you’re looking for. I think it’s perfect for your friend.
If you need more on the praxeology end, The Ultimate Foundation of Economic Science is probably your ticket.
If you need more in-depth Austrian theory, if you’re not up for just recommending parts of HA or MES, you might look into Economics for Real People, which is generally recommended as an introductory text, but at 350 pages, it may very well be sizable enough, and certainly goes into free market/Austrian understandings of economics. However, it may be not be high-level enough, as you fear for EiOL (although, even though the latter is generally recommonded as the first introductory text, Hazlitt does not exactly baby the reader by any means).
You might also check out:
The Foundations of Modern Austrian Economics and Classical Liberalism and the Austrian School (which I believe is based on the author’s short essay with almost the same name)
If you want to browse shorter supporting material, see here.
Lemme know if you’re looking for something of a different angle.