Cheap Ar15

Bushmaster ORC

Often see the Bushmaster ORC (Optics Ready Carbine) for sale under $700

The best AR for hunting for under a grand is the DPMS Oracle 7.62. But it is an AR-10 in .308/ 7.62 Nato:

DPMS Oracle

DPMS Oracle also comes in a AR15 configuration...with about a $650.00 price point... 
There is also the DPMS Sportical - no dust cover or Forward Assist...
(MSRP is $1099, but you can get it retail for $950)
If you MUST have a .223/ 5.56, then go for the Bushmaster

Bushmaster CAR15 223 16 BSH REDDOT

The Bushmaster Carbon15 is a cheap priced AR15. With a price around $700-$850 (depending on where you are pricing it at). They are very lite. Weighing in at only 5.5-5.7 pounds make this a pretty good selection for any AR shooter. The new Carbon15's have been upgraded in all the problem areas and are surprisingly a good AR for the money now.

Right now with the price of AR15's out the roof you can't go wrong with a AK-47. You can pick one of these bulletproof AK-47's up for around $500-$700 and you cant go wrong.