3-9X40 mm is a great choice for the Optima since it is able to shoot out to 150 yards or better with PRACTICE and the right projectile. For a low cost scope I would suggest you look at the Bushnell Banner Dusk to Dawn Scopes with 4" eye relief. They can be had for about $65.00 and the optics are excellent in my opinion. They are also fog and shock proof and best of all have Bushnell to back them up. Bushnell has been in the business for many years now. They make a good product and do not charge an arm and a leg.

If you sight in for a couple inches high at 100 yards you could make further distance shots if you practice. It is good to consider how far your average shot is in the area you hunt and sight in based on that information. For instance, most my shots are between 50-100 yards where I hunt, so I like to sight in for 75 yards. That way I am never far from the money shot and can put my projectiles, with practice, where I want them to hit. Even in tight situations.

Check out D & R Sports for a Bushnell Banner. They had some real good prices last time I looked.