This could be something that you bought for a higher price than what most people would guess based on the item, or it could be something you bought for a normal price that has gained significant value as time has gone on.
What made me think of this question is a LEGO minifigure I got with my “The Hobbit: An Unexpected Journey” disc. It is Bilbo Baggins in a blue coat that was apparently only sold in that movie box only at Target stores. Even considering the exclusivity, I would have guessed maybe $10-20 for such a tiny piece of plastic, but there are sold listings on eBay from $80 to $225. I could possibly even get towards the higher end of that number since I still have everything in the original box in good condition. It’s not worth a ton compared to some other items people may own, but I think most people would not expect nearly that amount.
Moderate condition, ex-library so there are stamps and labels. However it’s about 120 years old and a first edition. There was one for sale last year, now there are none for sale anywhere in the world, AFAIK. It was the first book of its genre and is recognised as influencing the later masters. Think Poe influencing Conan Doyle. I’m reluctant to mention the details because I don’t want it showing up in a search. Sorry to be so cagey! I’d be annoyed by this post myself if I read it.
No worries don’t doxx yourself, I’m happy you got to enjoy this book, I can see how happy you are when you talk about it.