What Briman said... I built my first AR earlier this fall from a very early DPMS stripped lower... With a DPMS LPK and TAPCO collapsable stock I had a complete lower done in about 25 minutes... With printed instructions as a guide from AR15.com.

I priced parts seperately vs a completely assembled upper and the price wasn't much different by the time I bought tools so I went an assembled DPMS upper route. 20" bull, free floated barrel, forward assist, flat top... 2 pins and she went together. Runs 100% with both factory 55gr Rem green / white box, IVI (Canadian) 5.56 NATO as well as my own 55 gr Nosler BT handloads... I have achieved 1/2 MOA with my handloads thus far...

My barrel is chambered for 223... 5.56 NATO causes an over pressure condition in it but I just had to try some to be sure... Be aware of this... There are some good articles on who what and why of this issue... I have no ruptured primers but they are flat as a pancake and the ejector button peels brass on the headstamp due to tightness of the case in the chamber after firing... Therefore I feed it properly...

I have right at about $700 into this gun (parts + shipping costs) less the bipod, millet rings and the Leupold that I had on another rifle... My 03 FFL gets me dealer pricing at places such as Midway USA & Brownells and saved me a couple of dollars on the LPK and stock, somewhere in the neighborhood of $15... Saved nothing on the upper as it was on sale (at dealer pricing).

Hopefully that gets you an idea... It's easy to do...