For me, it was a pair of merrell shoes on sale. They have lasted 3+ years, have great grip in the snow and ice, and so comfortable, my feet don’t hurt after wearing all day.
Never cheap out on anything that comes between you and the ground; shoes, tires, a bed.
What have been some of your good purchases under $100?
A foam mattress topper. Really was a lifesaver for a while when I couldn’t get the whole mattress replaced.
Also, a tire pressure gauge. Had to use that thing more times than I could count through the years.