Yes I think they are about £10 each.
I cannot stress this enough, prioritise the A2 over the AS, start revising for the AS retakes around March/April it is very manageable.
Make sure you use physicsandmathstutor.com, do all the questions by topic for all the chapters before you start on past papers so you identify weaknesses otherwise past papers will be useless. This is for maths.
Don't memorise for biology/chemistry. Use youtube videos in order to achieve solid understanding.