Well, you have several options that will ring in at right around a 100 bucks or so.
For a tube scope with magnification, I would recommend the bushnell trophy with the turkey plex reticle 1.5-4X32. Very good, rugged scope.
If you want a red dot tube style sight, I would recommend the bushnell trophy red dot. Very rugged, accurate sight. Can be had for under 100.00.
Lastly, the Mueller relfex sight is a non-tube sight with an unlimited FOV, and is also very rugged.
The choice is really yours. I would recommend checking out
www.opticsplanet.com they have free shipping, and you will be able to take a look at all of them and decide for yourself.
I have used all three, and all will get the job done effectively.