For reasonable cost, simplicity, and function, I'd start with the first build in this thread with a couple of changes:
1. Shaw's unported 223 Wylde barrel (wasn't available back then - thanks to
@StupidLightweight and the people in this thread for making that happen).
2. Either a Kaw Valley PCC handguard of you choice (relatively inexpensive and very functional) or if you want something a little lighter still, one of the homemade versions people are doing here. (My 9" handguard is only 1.9 oz and probably 1/3 the cost of the Kaw Valley and just as rigid)