I have a 3-9 x 40 Tasco Golden Antler air rifle scope that I mount on my grandpa's Marlin rifle when we go shooting. It's great, it has zoom, parallax adjustment, large knobs, and easy to read markings. You can get one for around $40-50
This. Got it a month or so ago. Comes with rings and caps. Bushnell 3-9 rimfire $37: (make sure to select the super saver shipping and you'll have it in a week or less for free shipping - comes from KY)