Perhaps a good metric for how much this should be worth would be to ask whether buying this book for a junior developer with your own money would save you that

Perhaps a good metric for how much this should be worth would be to ask whether buying this book for a junior developer with your own money would save you that amount in the long term. Based on the article only, and the amount of times I've personally had to have similar discussions, I'd say it's worth that amount at least (and likely more).