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 went to a Hotel Furniture liquidator for some new furniture. Saw a good looking office chair and they only wanted $20 for it.
Brought that bad boy home and only then did I find out that they had sold me a new Herman Miller Aeron for only $20. Completely insane.
The single most expensive item I own is a gold coin from Imperial Rome, an Aureus of emperor Antoninus Pius. I bought it about three years ago when I was just starting to collect ancient coins. I came across this particular coin on a “regular” gold & silver bullion site in my neck of the woods, for 3K. Not knowing too much about it, I bit the bullet (which is actually an incredibly stupid thing to do, akin to gambling). Turns out it’s very real, mint state, and worth about 2K over what I paid for it right now. I have since continued collecting ancients, especially Romans, and by now know the entire history of Rome and all its emperors in detail. Which again underscores how incredibly stupid it was to buy something so expensive without decent prior research. I was just incredibly lucky that an actual reputed bullion dealer apparantly had come across this coin and got rid of it far under what it was worth.
I don’t expect to be able to repeat this feat, but I’m definitely on the lookout…
I had a friend over who complimented my teapot, I love it because it’s a nice color, good size and has a stainless steel infuser that fits inside. So I offered to get her one of her own only to find out that this particular color is highly collectible and worth 6-7x what I paid for it originally. Now I have a nice teapot I’m paranoid about anything happening to, haha.
I have four tyres in pretty good condition on my car, that’s $1000 right there.
I had a free book reward from Thriftbooks, which I used for a copy of Long Dark Teatime of the Soul by Douglas Adams. When it came, I was kinda bummed that some kid had scribbled on the title page, but eh, it was free. At least it was a first edition in otherwise good condition, I won’t complain.
As I was reading, I got a little itch in the back of my mind, and it of curiosity looked up his signature. Turns out, it looks like some kid’s scribbling
Probably why no one realized.
So I got a signed first edition, which goes for about $200, totally free.
I collected Marvel cards back in the 90s and I’m pretty sure I have at least a few that are official “collectors items” now. I’ve never looked into it very thoroughly since I just kept them in baseball card pages with no other particular protection from the climate, etc, but who knows?
I have some football cards at my parents house that are in the same boat. Maybe take a look through them to try to estimate prices and protect the expensive ones. IDK about Marvel cards, but I know there are apps for some other trading cards where you can just scan a picture of the card and get an estimated price based on recent sales.