Hmm... I would definitely buy it, I'm keen on your insight into things. Also, your spec solutions were superb for the exam from 2010, it really helped me to understand where I screwed up.
I tutor, so it would be really useful for myself to show these sorts of materials to the students I work with, etc.
Ideally, no more than $30. However, to self publish something like this, you're going to need a lot of time and patience. 450 pages at Officeworks is looking at about... ~$14 each copy, just for the paper and ink, provided you print more than 12 copies at once.
Postage and stuff would also need to be taken into consideration, as well as your release date, and known buyers. Overprinting could be a costly mistake.
However, I would definitely buy a copy or two, provided it is at a reasonable price.