I built my AR15, but opted for an assembled upper. All parts bought from Palmetto State Armory.
Their deals are a hit and miss, but this one is still available on there website:
$100 - Palmetto State Armory Blemished Lower Receiver
$700 - PSA 16'' Hammer-Forged Mid CTR Rifle Kit - AR-15 Parts Sale - AR-15
And stock up on some magazines too: $90 - PSA D&H 5.56mm 30rd Aluminum Magazine - Black Teflon, Foliage Green Follower 10 Pack
As far as instructions, I used a couple of Youtube videos. There are ton of them available, but I found these two most helpful:
How to Assemble an AR-15 Lower Receiver. Video from Ares Armor, home of the 80 percent lower. - YouTube
AR15 Lower Build - YouTube
And I used the brass hammer to start the roll pins, but finished using vice grips wrapped with tape.