Several titles in Edward Marston's Railway Detective series, all at £1.79, unless otherwise indicated. Again most/all are repeats.
The Circus Train Conspiracy, #14, £1.49:
https://www.amazon.co.uk/gp/product/B06XXVTSD3/
The Excursion Train, #2:
https://www.amazon.co.uk/gp/product/B006WB7MC0/
Railway to the Grave, #7:
https://www.amazon.co.uk/gp/product/B006WB7GP8/
Timetable of Death, #12:
https://www.amazon.co.uk/gp/product/B00TCZP73O/
The Railway Viaduct, #3:
https://www.amazon.co.uk/gp/product/B006WB7MXO/
Signal for Vengeance, #13:
https://www.amazon.co.uk/gp/product/B01E5LHD7C/
And in Marston's Home Front Detective series, #8,
The Unseen Hand:
https://www.amazon.co.uk/gp/product/B07G4L4VR8/