Is "Of all the things money can't buy, law isn't one" grammatically correct?
It's a (grammatically correct) double negative saying that something (law) is not a part of a group of things someone can't do... -.-
So, if we flipped each one (you have to be mindful of maintaining semantic balance when you flip double negatives), we would end up with a sentence like:
Of all the things money can buy, Law is one (of those things).
Or, more simply:
Money can buy Law.
There are subtleties lost in such a direct of form expression, which is why the author chose to convey the message in their quasi-litotic style.
It is grammatically correct, but nonsensical. Because of your use of the word all.
The construction "of all the blahs" signals to the reader that you are talking about a group of things, that are all blahs, from which you are about to single out one thing to compare it to all the other things in that group. You are about to explain how there's that one blah in that group that is different from all the other blahs.
- Of all the primates, gorillas are the biggest.
- Of all the palaces, the Louvre is my favorite.
- Of all the things I can buy, law is the cheapest.
However, in your case the comparison you are trying to draw is that unlike every other element in the group, the element that you've singled out from the group actually isn't in the group at all. And that just doesn't make any sense. You are stating two things that directly contradict each other.
- Of all the primates, crocodiles are not primates.
- Of all my favorite palaces, David Hasselhoff isn't one.
- Of all the apples in the basket, this apple is not in the basket.
- Of all my closest friends, Osama bin Laden never was one.
- Of all the gaming console manufacturers on the market, Reebok isn't one.
- Of all the things I cannot buy, law is a thing I can buy.
- Of all the stupid people on the Internet, you are not one.
This just doesn't work. At best it's rather comical, and indeed can be deliberately played for comedic effect. At worst it's utter nonsense.
If being funny is not your intention at all, which given the topic it might or might not be, then you need to reword.
Edit in response to comment: Yes, you can also expressly use this construction for surprise effect "to highlight the Purchasability of Law". Observe:
- Of all the things money can't buy, law is the one money can buy most easily.
- Of all the things money can't buy, law is the one with the lowest price tag.
- Of all the things money can't buy, law is on sale most often.
Or any number of other alternatives. This actually has the punch you're after, and makes it clear that it's a point you're deliberately making. What you have right now is muddy and raises the question if it's deliberate at all, just a typo, or lack of sufficient command of the language.
I'm going to echo the answer provided by tidbertum but present it in a graphical fashion.
And to paraphrase the original sentence, with some styling and emphasis:
Of [all the things that money can't buy], law is not one [of those things].
To further echo tidbertum and analyze the meaning of the sentence, because it's not one of those things that money can't buy, it is, logically, something that money can buy.