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.
My two most valuable records are the Katamari Damacy vinyl from Fangamer & the Sonic Adventure 2 vinyl from Brave Wave. I got both for $40 at different conventions and they’ve never been re-pressed so they both go for $250 sometimes, even used.
Game memorabilia is a weird niche, but there’s definitely a market for it. I have a few games on my bookshelf that would sell for ~$250. Cuz I was an autistic kid who made sure to keep all of the original boxes, box art, game manuals, etc (because it bothered me when they weren’t complete.) So a lot of my childhood games are actually worth a fair bit of money now. Retro games are stupid expensive, cuz everyone either knows what it’s worth and is hoarding their collection, or in their 30’s and 40’s (which means they have enough money to afford the exorbitant over-inflated costs) while trying to relive nostalgia.
It’s also interesting seeing the discrepancies in prices across different consoles. I own the same game on both PS2 and GameCube. The PS2 version would only sell for ~$30, but the GameCube version would easily sell for closer to $150. Simply because the GameCube version wasn’t as popular, so there are fewer copies in circulation. It’s functionally the same game, but because the PS2 dominated that console generation there are more copies of PS2 games in circulation.