Recently went through this same drill for my M&P 15 22. Didn't want to sink a lot of money in to the scope, since I would be replacing it with a SWFA 1-6x. Rifle's purpose was primarily as a training tool.

http://swfa.com/Optisan-1-4x24-Mamba...bo-P51887.aspx

Another good option is the Vortex Diamondback line. Doubt parallax will be much of an issue given your targets and ranges.

http://swfa.com/Vortex-Diamondback-R...pes-C1409.aspx