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.
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
Visited Japan last year and picked up all the originals in Japanese. Red, blue, green, yellow, crystal, gold and silver. Solid condition and working for a decent price at an out of the way recommended shop. I would like to pick up the boxes but they would probably be more expensive because of the rarity. I'll probably end up buying some aftermarket on Etsy just to display them.
It's so strange to see those cartages worth so much. But good on you.
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.
Yes, Pokémon games, some Lego sets, and a few random niche books have all gone up in value in ways I couldn’t have predicted.
If you ever go to Japan save up some good money for collectibles. They're sold at VERY reasonable prices and because it's Japan and people take care of their shit they're in very good conditions a lot of the time. You'll want to buy a lot of your childhood stuff, I know I did. I had to buy an extra checked luggage just for all the stuff I brought back and I only traveled with my carry on because I wasn't expecting to buy anything except for a game cube which I could fit. Turns out I was wrong.
TIL I have like $300 of Pokemon games sitting ony shelf. I still play them sometimes on my childhood Gameboy