Scopes are like AR's, there are tons of them. The aimpoint is just a red dot so scrap that. Personally Id never buy a red dot and think they are a waste of money when I can do the same thing with iron sights. 200-800 yards is a pretty big range. If I was shooting those varying distances Id pick up a variable scope from 3-9 to a 4-16 power.
If most of your shots are going to be under 500 with the occasional 800 yarder than just get a good 1-4. 1-4 scopes are my favorite for an AR15. You can pick up a pretty decent one like a Millet,Nikon,Burris for around $250-$350. I used to have a Leupold VXR Patrol 1.25-4 on my 20" A4 and absolutely loved it but it cost almost $600.
You just need to go down to a store like Cabelas, Bass Pro, Sportsmans Warehouse..etc and look through a bunch.
Personally I wouldnt put anything bigger than a 3-9 on an AR but thats just me. If I want to bang out to 800 Im grabbing my 308. There isnt a wrong answer though. Just whatever you like is the right answer, just dont by a chinese made scope (some are ok but most arent). Vortex puts out great scopes for the cost. Throw a 3-9 Vortex diamondback on it (its like $200)
But for all around use from quick up close to way out there, you cant beat a 1-4 in my opinion.