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.
I don’t own them anymore, but vintage Hewlett-Packard calculators, the RPN variety for engineers. An acquaintance moved into hospice a few years ago, and his family cleared out the house. I went over because they offered us sailors pick of his old boat gear, but I poked through the pile of electronics destined for the recycler, too. I grabbed several old calculators, a printer unit, and some programming books for them, as I was vaguely aware that maybe some people collect them. As it turns out, I got almost $700 for them on eBay.
The ones that I do still own are several IBM Model M keyboards that I picked out of the $1 keyboard bin at the university surplus shop back in the day. Although, after using one of them for 17 years (with no signs of wear), I realized that 5 spares would long outlast me, I sold a few for almost $400 total.
Another friend unexpectedly passed away earlier this year. A neighbor is helping to liquidate his vintage computer collection. I stopped by the house and saw a Northgate OmniKey Ultra in a pile, and asked how much would he take for it. Turns out, that was a recycling pile, so he just gave it to me. I could probably get $200 for it after cleaning it up, if I didn’t need it.
Seething with jealousy I am. I love the HP 33s but it’s currently priced more than I’d like. I don’t know if I’d actually use it, not a ton to use it on anymore, but wish I had one nonetheless.