A Burris Fullfield II 3X9X40 with ballistic plex cross hairs is what I have on my varmit rifle. They are just under $300 and would be good for the ranges your looking for.

You can also get it with mil-dot cross hairs. As Tom stated you can spend a lot of money on optics. I however would at least drop around $300 on what I and the others have said. Don't buy some $100 tasco or bushenell POS.

http://www.burrisoptics.com/fullfield.html