The title says it all but the internet should be used by parents and children to get the revision books needed and why? – because they are cheaper online.
For years primary and secondary schools have said you can order all books through them together and this is the easy option. The books your children need are on loads of different websites for a fraction of the cost delivered to your door. You can also get even cheaper options if you get second hand books or you can gain money back on your revision books by using trade websites to sell on after.