I became very interested in Austrian economic theory in college and even went so far as to read Ludwig von Mises' tome Human Action cover-to-cover. I also took a couple of courses in economics but generally found them unchallenging, misleading, and perhaps worst, uninteresting. Whereas the courses were dominated by simple calculus math problems to "solve" contrived (and unrealistic) scenarios, the Austrian approach is essentially without math. Instead of math, there is philosophy, logic, and analysis.
Austrian theory can be expressed in plain English (though occasional graphs can help illustrate concepts), and I believe it is appropriate for high school aged students and perhaps even advanced junior-high students. In particular, I would recommend Gene Callahan's book Economics for Real People as an effective and breezy introduction to economics. Another good choice would be Henry Hazlitt's Economics in One Lesson. One or both of these books could serve as the basis for a first course in economics for homeschoolers.
However, some good news from Bob Murphy, an Austrian economist, is that the Mises Institute is moving forward on a project for him to create a high school course geared especially for homeschoolers. Read about it here. While I am a little concerned about the result being "too mainstream" I have no doubt that this will be a worthwhile course and a boon for homeschoolers.