Well, magnification is a personal preference. in the Nikon M223 line, 2-8 power or higher would be my thought.
You can also look at Vortex scopes. They are in the same price range, and they are a lot of scope for the money. Opticsplanet.com has good prices, usually free shipping as well.
The viper line is their high quality, reasonable price line. Viper PST is a step up. I have the 1-4x 24 version on my AR. Again, power is a preference.
I don't think you can go wrong with either. Spend as much on the optics/mount as you think you can afford. It will make you happier in the long run.