Welcome to the fun.. oh and the forum! :mrgreen:
OK seeing as no one else has replied, I'll add my limited knowing...
1. Most Red Dots and Holo Sights of any quality are going to run 100-300 more than you've listed as available funding. By quality I'm talking about the two big boys in the Red Dot and Holo arena which are AimPoint and EOTech. ACOG is well and away from your price range by several hundred more dollars than the other two.
2. I'm not totally sure, but I'm pretty sure that both of those have no additional magnification without an add on piece that costs about as much as the optic itself... pretty sure.
3. If you're simply looking to get out to 300yrds and don't want a large optic, try one of the lower powered fixed mag optics. Nikon, Burris, Bushnell all have contenders there. This is a huge market so those three aren't the only contenders.
I know that with the way I shoot, both of those are really only of any value at the sub-100m ranges, but that's me... if I need to go further I either use the Iron Sights or switch weapons.
Now some other fun notes.... you have the ES2 so if I'm remembering this correctly it's an A2 style upper with the perm attached carry handle. That means having an optic that is mounted there. You'd want to get a Picatinny rail that mounts to the carry handle.. those are fairly inexpensive. You'd want low rings, quick detach most likely as well. Then you're also looking at some sort of cheek rest as well. Again, a lot of options, take your pick and they won't break the bank.
There is always the classic scope for AR's.. someone will have to remember what they are called, but they are magnified but something like 4x if I remember right, come with a mount and work rather well from my experience.
Was there a reason why you wanted to look at the Holo and Red Dot's verses a traditional optic?
Hope that helps..