Has anyone ever found something rare or expensive for a good price?

No

My brother got an iPhone 5S for $18

I have, got a 350 dollar wrench set for 30 dollars.

I personally have not but i have found some pretty cool things there. I usually go for the farmers market. I buy roasted chilis and lots of produce at an amazing price. Bonus if you speak spanish.

There sellers are pretty savvy, but you never know when you might find a diamond in the rough