The Strikefire is a SOLID optic. One of the best to come out of China, IMO.There was discussion of the Vortex Strikefire here recently...
Most guys seem to be pretty happy with them and they are reasonably priced. A couple guys at my private shooting club have these on their AR's and I haven't heard any complaints.
If you're prepared to drop $4-500 as you noted, I believe Eotech offers a few models in that price range and they are generally well regarded in the AR shooter community. The Meprolight M21 can also be found in this price range.
Bushnell makes an "ACOG style" scope for sub $200 but I have no experience with these other than superficially they look kind of like an ACOG.
The Primary Arms micro has a better reputation that a sub-$100 red dot deserves. PA's customer service is outstanding and the PA micro's are reputed to be VERY reliable and rugged.
If you're looking to spend more, the Aimpoint Pro or EoTech 512 are hard optics to beat. I run a 512 on my home defense carbine and I love the thing. At the Camp Perry rifle pop-up rifle shoot, I was able to make COM hits out to 300 yards with little difficulty. I'd assume one could do the same with a properly zero'd Aimpoint Pro.
The Lucid HD7 is also VERY well regarded and comes in at just under $200, as I recall.