well i do biomedical science, so the textbooks I use are pretty much almost essential - to me anyhow because the subjects I am taking for my degree all mingle into each other so the books I pay for I am going to get my moneys worth, but yeah the price tag is pretty outrageous, so i just pay for half then get my mum to pitch in the other half for the book - cant go and buy the textbooks on youth allowance - nuh uh
not sure what it is like for other courses.
If you are lucky you might be able to score some second hand ones from the student association or keep an eye out for flyers in the library or on campus - which is pretty much non existant for science textbooks anyhow.