Platform 5 also includes track machines don't they now? They are indeed very high quality, but jeez hasn't the price gone through the roof?!
NREA, ST Publications and AEB all do most acceptable versions for much less. I believe the ST Publications version is only £13 but includes things like Underground, Northern Ireland, Irish Rail, track machines and more too. NREA's book is pocket sized, with the 2014 version due out in the next couple of weeks if not sooner. Very good value for £9.95 but their previous versions (I've owned most of them from 2004 to 2012, not bought one lately) haven't included things like track machines or Underground. That could well have changed in the 2013 or the forthcoming 2014 version mind. AEB's UK combined I've not bought in years but it was pretty good for £8.95 when I bought it. To be honest I had assumed they'd stopped doing it as I hadn't seen it in the shops for a long time.
If you're going for the books in Ian Allen, I'd recommend trying the Manchester store over the Birmingham one, their stocking seems to be better. And heart-of-wessex will probably remember as much as me how bad the Cardiff store went a few years back, so much so I stopped bothering trying to get owt in there, not even browsed there for years!