Wat were the official questions like? I was gonna think of buying them......
Well, they give you a feel of what the test will be like - and would probably be the closest preparation materials relating to the actual test (since, of course, they're produced by ACER).
It's a bit pricey for the (not very many) questions in the books (I think there are ~50 for the "practice questions" volumes .. can't remember how many were in the red book labelled "practice test" but there were more).
Best thing to do is to find someone who owns the books and borrow them for a bit - minimises your expenses

.
If you can't do that, I think it would be good to buy them anyway. Just so you don't feel underprepared and become anxious on the day.
I think timing yourself to finish is crucial too. They give you set times in the books so that helps...
er here's a sample Q (section 1):
A recent study has shown that when food plants such as corn, strawberries and marionberries are grown without the use of insecticides or herbicides, they have significantly higher levels of cancer-fighting chemicals than those grown using pesticides. These chemicals, called
phenolics, also deter attack by insects. The use of fertilizer boosts phenolic levels in plants.
The report of the study implies that
A - what is bad for insects may be good for humans
B - penolics may lead to an increased cancer risk in humans
C - increased fertilizer use on plant crops increases the likelihood of insect attack
D - for maximum phenolic levels in a plant, farmers should use minimal amounts of pesticides and fertilizer.
Answer:
[A]