There’s a lot of lore regarding Tolkien’s world, I easily could have missed something. Many other universes that use magic definitely have a quid pro quo cost for that usage, and I wouldn’t be surprised if there were something in the LOTR universe that mentions it in passing. There’s quite a bit about Gandalf’s magic usage (or mostly lack thereof, for such an incredibly powerful character his usage is very sparing) and I’d be curious if there’s a canon writing from Tolkien that backs up the reasoning for that, like loss of life energy or whatever.
If there is, it’s not in The Hobbit or LotR itself. Silmarillion is impenetrable to me, so idk.
I’ve read the Silmarillion twice, and it’s sort of the “Genesis” story and Old Testament of the LOTR world. All the Old Gods, their squabbles, creation of Elves, Dwarves, Men, etc. I don’t think I would have missed the exchange of magic for life, though there is definitely an inferred consequence that use of magic takes a toll like overexerting oneself, especially when battling another magical being, but that seemed more of a plot tool used to arrange characters as needed. Plenty of evidence that baddies keep coming back and get stronger, and also some evidence that lack of magical beings in the world makes the world less magical as a whole - iow, this world doesn’t have permanent magic affixed to the place, it almost seems like it needs believers and practitioners for it to exist, and as they die or depart West, magic ceases to functionally exist along with the “ascent of Man” at the end of LOTR.