I like Leupold optics, you can find them for under $300. The glass quality is wonderful. I would really recommend a 1.5-4 Firedot made by them, but you will pay a little more than $300. Wonderful customer service as well.

Tommy, I recommend this AR Ballistics Calibrated Scope : budsgunshop.com/product_info.php/products_id/712016913/bus+ar+45-18x40+blk+wind+hold

Hi,
It really depends on how much magnification you wanted but Primary Arms 1-6x ACSS (on primary arms web) is absolute amazing for this (and less than $300). I hope this helps.