If you want to build (it's easy and enlightening, especially with the help of YouTube; and will require about an hour of your time), this is the ticket:
PSA 16" CHF middy rifle kit: $509.99
Add $150-200 for a stripped lower + rear sight, and you're in business. Why is this better than the $750 complete rifle you can buy elsewhere? It's almost certainly got a far superior BCG and great barrel (the two most critical parts), midlength gas, and a milspec platform that is more worthy of investing upgrades into, IMO.