$700 is pretty low
probably possible if he gt a good deal on the lower receiver and the barrel and just throgh the rest together
but like Howler said you WILL need a trigger job
i have 2 ar's and the 1 i carried when i served all had terrible triggers
$200 chip mccormick solves the problem and they are super easy to drop in
but $700 is a little fishy
see if he has a rig already built and if not ask where he gets his upper/lower receiver and barrels from