Just a note - I looked into getting copy of Perry's Chemical Engineering Handbook then realised that they fetch £130!!!
I know it's simple but, remember to check auction/secondhand sites (we all know the ones) for what you want.
Managed to pick the 8th edition of this book up in mint condition for £40! Definitely deals to be had.
Oh, and if you're in Manchester and try to get hold of this book through a library - good luck as the only copies in the entirety of Greater Manchester are a Reference copy in Boston and Salford as well as a copy at Manchester University Library.
Be warned though as expect membership to Manchester University Library for the general public to cost £75 per year!