You can snag a used aimpoint pro for about $300. If your life could be on the line, how cheap do you want it? As far a proven quality optics go, $300 to $400 bucks is no where near an arm or leg, its the bottom end of the rung.
Greg prefers spending his money on stuff like this..... http://www.thetacsac.com/products/the-tacsac