What I have done is look on eBay and pick up each individual book, some used, some new - it doesn't matter. Instead of the £25 pound per book I have been picking them up for about £7 delivered. If you plan this strategically then you can pick them up in series of how you will study for them, rather than getting them all in one go.
I use the AFE ones, purely because the first one I got was PPL 1, therefore the rest would create the set. Just make sure they are recent if you are going on the eBay route.
If, for example you look here -
AIR PILOT'S MANUAL FLYING TRAINING by TREVOR THOM ( 9781843360643 ) - Books & Audio Books at Pickabook.co.uk the Trev Thom books are very cheap on that website new. Probably work out cheaper than a kit. Build it up over time
Because my finances are not infinite I thought saving £100 would go nicely toward a lesson. Each to their own - you may want a set of nice shiny new books. If so, when you have finished with them they WILL go on the bay with ease...
BTW, anyone with AFE Meteorology PM ME
<-- Last one to get!