I've built one a month ago and I'm helping two friends build one this week. They are budget builds but they'll still be nice guns. Obviously 556 is the most economical way to go but I'm not sure you want to go that route for hunting. 300B/O is another route if you're ok with 30/30 type ballistics which is fine for deer if you plan on hunting with it.
I've been able to shop around and send links to my buddies to order. I think the prices have been $500-$600 for everything. I have purchased mostly Anderson upper and lowers. I think I paid $49 for the lower a couple of weeks ago from Primary Arms. They were out of stock and I signed up for email alerts and they notified me they were back in stock.
I've purchase a ton of barrels from Stone Mountain arsenal in Georgia but the last I checked they were almost completely out of barrels. While they're very inexpensive they've performed really well for me.
I purchase a lot of stuff from Outdoor Sports USA. They got a bunch of stuff. Free shipping with no minimums too. I've purchased, upper and lower receiver parts kits, buffer, springs, and tubes, stocks, grips, muzzle devices, hand guards, and gas blocks/tubes.
I have purchased most of my BCGs from Palmeto State. Usually wait for them to go on sale but that's not been the case lately so I've been purchasing them wherever I can find a decent deal.
Good luck.