You can build a much nicer one for $600 (that's just basic) with some patience of course.
The hardest one to find for a cheap price (IMHO) is the upper with a BCG (Bolt carrier Group) and Charging handle.. I got my complete Rock River Arms CAR 16" barrel upper with BCG from GunBroker for $420 something with shipping, and I'm pretty sure you can find a complete lower for as low as $130... but I would try to build the lower to your specs... Here's a a pic of mine.
I spent more on the add on's:
Tango Down VFG and pistol Grip $50 off this wonderful forum
Matech Buis (rear site) ebay $40
Mapul Moe Carbine handguard $30 off Ebay
Magpul MS2 $28 Ebay
Bushnell Trophy $50 craigslist
Magpul CTR butt stock $70 off this wonderful forum
Magpul bad lever $20 or something.. forgot where I got that one.
5 Magpul PMAGs (M version) $70 something off Bravo Company site.
Magpul advanced trigger guard $10 or something off this wonderful forum
Now from a $600 basic rifle I got's a $900 plus dollar AR... and it isn't stopping there...

Hope this helps...
