I like Sophia's answer for many reasons, but think Lasyah hits the nail on the head: the value of security is relative to what you're trying to secure. I work in IT. If you're asking about IT security, it's value is paramount and you measure it by your success to date against being hacked. I say "to date" because all businesses are sitting ducks. I've always told my small business clients that you can spend $10,000US and feel fairly protected from 80% of the hacker world. You can spend 100 times that amount and be protected from another 10%. No one has the money to be fully secured against that last 10%.
I read your bio and would like to see your answer to this question.
You can't improve security if you can't measure its effectiveness. - Amrit Williams (security expert and blogger)
If it works and protects, then it is functioning well. The moment it fails is the moment it needs to be improved and upgraded. Until then, you can't measure it with a yardstick.
The value of security, it sounds a bit vague at the moment. Security in our privacy? Our lives? Our reputation? Our family? Our assets? Our mental health? Our human rights? Our planet?
If it is any of the above, there is no universally accepted price on those things.
The question shouldn't be how do we measure the value of security. instead, it should be how much value do you place on your assets determines how much security you need.