$100 is on the edge of the "nothing but crap" category IMHO, but there are a few decent options.
Bushnell Banner Shotgun/Muzzleloader Fixed 4x
- I have this scope and it has held up to a couple years of bouncing around strapped to my quad while grouse hunting. Holds zero well even after all that, and still puts 10 rounds into a single hole at 25m on my CZ 513.
Simmons 22 Mag Fixed 4x or 3-9
- I don't own this scope but have thought about it many times. I have read tons of positive reviews on this scope, and apparently they hold up really well. In your price range this would be a good option. I chose the Bushnell mentioned above instead based on previous experience but almost gave in to the good reviews.
Personally these are the only 2 scopes under $100 that I would even consider, and I would be tempted to stick to a fixed power scope just for the reliability and lack of parts to break.
A fixed 4x is all you need for plinking at 50m and less.