If you have the knowledge to build your own you can do it pretty cheap. A parts kit with a 20 or 24" willson air guaged match or varmit stainless bull barrel will run you just over $500 and you just need a stripped lower of your choice to build it on $90-$150. The upper will come assembled, headspaced, and test fired. If you don't want to mess with the springs etc. you can buy a complete lower and complete upper still save a few $$ over buying an assembled rifle. The DPMS and the Bushmaster are good choices if you go with a complete rifle.