Stay away from kits (with the exception of CMMG).
Only option in that price range would be DPMS. Used, you could find a Bushmaster or RRA.
If this is a range toy, the above options should be fine. If this is for business, get an AK.
See, to get a good AR, takes a certain amount of $ and that's just how it is. The same is true of an AK or any other platform. The thing is that for less money, you can get the best example in a different platform. You can get a very good AK for $700. You cannot get a very good AR for $700.
It's always better to have the best example within a platform than a lesser example in another platform. That's my belief.