If you haven't already decided on a scope, I have the Nikon Prostaff 3-9X with a 40 mm ojb. If I remember right it was around $300 I am happy enough with it, the optics are quite clear but its not a Leupold or anything, and really you are only shooting a mini anyways. Normally the rifle sits in the back of my truck, and I am not worried about having to re-zero the scope even after driving down a bumpy gravel road.
Good luck with your purchase.