I went el-cheapo on mine since 1)I was doing it myself and didn't want to bust anything expensive, and 2)my wife wasn't exactly on-board with more guns in the house. Ended up with polymer Plum Crazy lower, CMMG upper, Olympus 16" SUM SS barrel 5.56, RRA BCG, VLTOR BCM Gunfighter charging handle, cheapo drop in rail, Magpul FDE furniture and a Primary Arms red dot (Aimpoint clone) on a quick detach mount.
OK, for the bad, the SUM barrel DOES NOT LIKE steel plinking ammo. Brass is great, but steel just gets stuck in there after about 30 rounds. I like the longer rails over the gas block and should've free floated instead of getting a drop in, but at least its fairly solid.
The good is WOW this thing is light. My shooting buddy has a full billet Quentin Defense AR and it is easily a couple pounds heavier than mine (although those QD lowers are sexy). Everyone gripes about polymer lowers, but I've had the gun together for a couple years now and have not had a single issue (besides, my Glocks are polymer). The Primary Arms red dot was $99 and it is dead on from 75yds in and tight groups at 100+. I would definitely check them out.