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 Still great, I just don't use it anymore since I feel it's outdated and loading speeds are better nowadays.
Hair clippers. I bought a set at Target for about $30 about 16-17 years ago after several bad haircuts in a row from the various chain barbers. I just have a simple men's cut and figured I probably wouldn't do worse than them and could always shave it off and call it a learning experience if I messed things up too badly.
It definitely took time to get decent at trimming the back and I had to have my wife help me sometimes while I got the hang of it, but at $20+ per haircut every 4-5 weeks, I figure I've saved almost $4k so far and it still works. I saved even more if my alternative was to pay up for a better salon to do the work.