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 good set of ear plugs. My toddler can be pretty screamy and I find it a lot easier to be a rational parent when I have ear plugs in that don’t muffle all sounds, but just take the edge off the loud ones.