I wouldn't go 2nd hand. How do you propose to ensure that the notes you buy are up to date nevermind being 100% complete. You going to turn every single page of them and check legibility/completeness? What will you check it against?
You have to enrol in a course anyway and undertake the required classroom training (consolidation) so why not start off with a squeeky clean set of notes now and then have access to the online forums and feedback that the various schools provide.
For the £1k or so as much as it hurts the bank balance it is quite small compared to what you are going to have to outlay during your flight training so better to bite the bullet now.