I agree that the individual cost of those books is very high. I am not sure how much of a discount you could reasonably get for a bulk buy either, so my estimate of getting to around £3 from the £15 or so individual price could be wide of the mark.

Employers have a 'duty of care' as a legal responsibility. It is generally thought these days that includes the mental health of staff as well as their physical health. If the organisation believes it does, it will look at all sorts of things. For example, my last employer mainly did it by placing a contract with an agency you could contact to discuss mental health concerns. It also subsidised membership of nearby gyms and things like that, under the umbrella 'duty of care' idea on the physical side.

Yes, you can certainly argue that should all be coming out of the individual's salary.