If you want to keep it around $700 order a Palmetto State Armory is your best budget but still reliable AR. It is "mil-spec". Some of the S&W and DPMS cheaper stuff are more "sporter" rifles. If you can squeeze an extra few hundred Walmart has the Colt 6920 for under $1,000 which is a great rifle.
Can't beat the PSA PA-15 multi. Handles as well as my M4 carbine I had in the service. Extended feed ramps, FN barrel, properly staked gas keys. Love it. Will never get rid of it.