My RRA
I just built a RRA rifle. I bought some of the parts used (the lower, upper, and trigger were all new) and built exactly what I wanted. I splurged in areas such as the tuned trigger and having it cut down and a phantom welded on to make it 16". (subtract $205 for those) I also already had a rear flip up sight and aimpoint so I didn't have to buy those.
RRA Rifle
complete lower $225 (ftf so no taxes/fees)
tan vltor $125
tan TD grip $26
RRA M4 chromelined upper $430
machine work and FH $90
WOA tuned 2-stage trigger $115
sold A2 stock -$60
Total: $951
Not bad for a rifle configured exactly like I want it. I think you can probably find some great deals out there for complete, already built rifles. And if they are configured exactly like you want, then that is the way to go. However, if you plan on doing a lot of mods, then I would recommend building it up yourself and only buying the parts you need.