If your school has the textbooks then on like the first page there should be a username and password which you can then use to login to pearsonplaces.com.au and get an online version of the textbooks. I think you can also sign up on the website without needing a username and password but I think you may have to pay for the online textbooks.
Book fairs and second hand book shops always have heaps of textbooks for cheap prices so you can do that if the above doesn't work