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 have a hideous lamp that I hate that’s worth about a grand. It doesn’t look like it’s worth that much, just a heavy brass base and reverse painted landscape shade… but all antique and sought after.
My cats are probably going to break it so I should sell it but it was the last lamp my mom refurbished before she died (why it didn’t get sold and I got it in the first place)
I also have a brass fairy floor lamp that, with no shade, is worth about $1500, but that one looks valuable, and is very rare (and super cool)