What's the cheapest thing you had bought that by the end of its usefulness made you say "wow, this was worth a lot more than what I've paid for!"
Mine... My Xbox 360 slim only costed 129 euro back in 2012 and to this day still work like brand new, you would think that the disc drive would stop working but no. Never had the need of open it or clean it's insides. Still great, I just don't use it anymore since I feel it's outdated and loading speeds are better nowadays.
I have some Shoes for Crews boots I bought back in roughly 2001-2. They're a little less waterproof higher up now due to some cracking (probably because they sat in a hot storage unit for a while), but I still frequently wear them today when working outside.
My old roommate got a window air conditioner for $20. I got about 15 years of use out of it until I had the windows replaced on the house and it didnt fit anymore. I sold it for $50.