Palmetto state armory, Cold Hand Arms, Spikes Tactical. Bravo company, and Ranier are good, but pricey. Gun shows usually have junk parts. Look at ar15.com, the industry sponsors have good deals or sales. You can always find good deals on that site.
Right now Cold hand has a complete Delton upper for $299.00, complete rifle kit w/o lower for $469.00 and a complete kit with lower for $609. That complete kit is what I bought on a sale for around $500 eight months back. I just checked their site and those prices are for real, right now.. I built my first with a Delton upper and Spikes lower with a full kit from them for less than $500.00 May have to pick up another myself for that price. As I picked up 3 lowers recently on sale at Palmetto for $57.00 each and they are waiting for uppers.
The internet IS the best place to find deals because you have so many companies to choose from.