They have the hardback of Girl on the Train in Asda for £7.00 at the moment, if that helps anyone.
I read it recently and really enjoyed it.
Of that twitter list, I've read The Silent Wife, Before I Go To Sleep, and Elizabeth is Missing.
I thought they were all good, so I will be looking at some of the others now. If I had to rate them I'd put Elizabeth is Missing as my favourite of the three, followed by Before I Go To Sleep and then The Silent Wife.
For books on the same lines I'd also suggest Harriet Lane's books, Alys, Always and Her, both of which I enjoyed. I preferred Alys to Her.
I've also recently read Don't Stand So Close by Luana Lewis, which was good but filled with triggering incidents.
And I've just finished The Ice Twins by SK Tremayne, which was okay but I think it lacked a bit of thinking in the plot and had a distinct "punish the bad mother" tone.