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.
Nintendo DS Pokemon Soulsilver with the Pokewalker. Worth a few hundred.
I walked into a used game store a year or two ago and saw the price of older Pokemon games and cried a little on the inside. I had a lot of the older games when I was younger that I sold to buy new games. I had Red as the earliest and stopped playing Pokemon after Diamond, so quite a few of the games in that timeframe. I unfortunately sold them before those games had such high price tags, but I never would have anticipated that when I sold them.
Not worth near what yours is, but I have red, blue, silver, firered, platinum, sun and moon as well as several on the switch. I’d like to collect them all but it would be very expensive