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.
The 10th anniversary Sonic the hedgehog crystal cube. Bought it on a whim back then, honestly don’t even remember what website I got it on, and when I got it I pretty much just kept it in the closet because I never wanted to put it out because I figured one of my cats would knock the damn thing over.
It was actually only a few months ago that I was talking about it when Sonic the hedgehog came up and I decided to Google it and I found out they only made 500 of the fucker.