Irons for sure have their place and should never be skimped on, but Irons are a HUGE set back in low light to at night time in my experience, maybe I am just not as proficient with them as I should be, I just cant see the buggards when it starts to get dark....A red dot of some sort is invaluable if you ever go shooting around astronomical twilight or nighttime.
have you tried the trijicon irons for an AR? I have them on my Bushmaster and they make target acquisition in low light much easier when relying on irons only. They would be in the price range of a $100 bucks too.