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?
Cheap Amazon bidet. $40 and it revolutionized my #2 experience.
These are magic, you can get good non-electric ones for $25 each and outfit your whole house. Three years from installing my first one I’m planning for power outlets near the toilets and saving for one that will yell at me in Japanese while it cleans.