Reddit mentions of Aim Sports 4X32 Tri III. Scope with Fiber Optic Sight

I haven't actually used it yet, but it seems very nice.

This is exactly what I ordered.
http://www.amazon.com/gp/product/B0052G6HPE/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

Just letting you know, that scope goes for $66 shipped new on Amazon

Not custom, just cheap and shitty

I just bought this scope http://www.amazon.com/Sports-Scope-Fiber-Optic-Sight/dp/B0052G6HPE

Then added a Star Red Dot scope on the side rail of the above scope. This one:
http://www.airsoftgi.com/product_info.php?products_id=16000

AR15s can definitely shoot at 400 yards with a good optic. It's at the edge of where you would need to start using match-grade ammo to squeeze out a little more accuracy and ballistic efficiency from the bullet.

Honestly, you can reach about 2-300 yards with some very inexpensive optics. You could slap a 3-9x hunting scope on there and go out a few hundred, or use a basic AR-15 specific scope for under $200. I have a $75 AIM scope that is entirely capable at 200 yards. It wouldn't be my first choice to carry into battle, but it's also a tiny fraction of the cost.

When you're going to 400-600, you need to look at bullet drop, and wind can start to become an issue, so you really need a tactical scope with accurate turret adjustments. This is where you start to need the higher quality optics. But I still think there are some options from $2-400 that will do the job at this range IF you have the skill to use them.

This is the $75, entirely usable scope that I can hit 200 yard shots with:

http://www.amazon.com/Sports-Scope-Fiber-Optic-Sight/dp/B0052G6HPE/ref=sr_1_9?ie=UTF8&qid=1458911546&sr=8-9&keywords=acog+scope

This $150 scope would be fine for a few hundred yards, and could reach out to 4-600 if you have the skill to use it:

http://www.amazon.com/Nikon-P-223-3x32-Matte-Carbine/dp/B006Z07JTE/ref=sr_1_11?ie=UTF8&qid=1458911357&sr=8-11&keywords=burris+ar+332

Here is another $150 scope that would probably be enough to do what you want:

http://www.amazon.com/Bushnell-Zone-223-Reticle-Riflescope-Parallax/dp/B00ABP4XDO/ref=sr_1_6?ie=UTF8&qid=1458911499&sr=8-6&keywords=bushnell+ar15+scope

I don't have any $1000 scopes on my AR15s, and I have little experience with them (although I know more about scopes for long-range precision rifles). So I won't comment any more than to say that I know Trijicon and other ACOG scopes are good choices in this price range, and will have more capability than the sub-$200 scopes I'm recommending.

(note: If you would never put an inexpensive scope on your rifle, that's cool. I'd prefer to avoid the "all cheap scopes suck!" argument.)