What is something cheap that is worth buying over and over.

Sometimes it's cheaper to buy something knowing it will break or wear out and have to be replaced regularly but it's still cheaper in the long run than the quality version.

I was looking at desk treadmills and someone mentioned that you can buy a high end one that will last a long time. But buying a cheap one every few years is better because it will take the expensive one a long time to pay itself off.