Benelli MR1 takes AR mag.'s, is a .223 semi. and can be bought new for under $2,000 (I think there's one in the EE right now for around $1,200+/-$100). Decent accuracy 2-4MOA with factory ammo., some have seen MOA with hand loads and runs reliably.
Also AR180-B semi. .223 that takes AR mag.'s and is probably the best option, but are not sold new anymore and can be hard to find. They sell for around the $1,400 to $1,900 range used and are a very good rifle with good accuracy and reliability, there are a few parts upgrades available too.
Cheers D