I have been doing this for a year now. I picked up two pounds of Unique and two pounds of CFE223 last week. On sale. (Psst, Wayne - I have your powder...)
Today at Cabela's I got two pounds of CFE223, two pounds of CFE Pistol, and 4000 CCI small pistol primers. With a coupon and a spare $25 gift card, it was just under $200 out the door.
It ain't hard to build up a couple of dozen pounds of powder and 20-30 thousand primers in a year, if you shop twice a month.
And yeah, I already have the parts for a half-dozen AR builds stashed. Just check Aero Precision, Brownell's, Sionics and BCM when they have sales. I'm putting away stuff for the grandkids now. My son and daughter were already taken care of five years ago. The magazine situation was taken care of eight years ago.