The Hornby catalogue might have some cheaper stuff though I expect there would be sighting issues on NR lines.
A network rail guy once told me that he was looking into ordering a CD/RA repeater unit for a station that drivers have had difficulty seeing the current one in sunlight and the unit cost without factoring in installation was over 7K.
I offered to build them a light with a cd/RA stencil in it for 6K but he didn't seem too interested in my offer!
I bought a ground position light signal from Dorman's 2 1/2 years ago, cost £950 for the complete LED signal