Picked up a used AR15/M4 a couple weeks back for $600....found it on backpage.com.
CMMG upper + anderson lower, 16" SS barrel, non float alumium quad rail, picatinny gas block....nothing special but compared to the 308 it's like a puny rifle and weighs next to nothing.
...I'm not completely sold on the carbon FRP uppers/lowers like the Bushmaster C-15 or the cheap Windhams quite yet - and I suppose it says a lot since I do a good amount of aerospace carbon fiber work.