From what I understand, this Will guy is Dr. Jeckle and Mr. Hyde. I have heard people say such great things about him and what a friendly person he is. The two times I have dealt with him, he has been less than friendly and I havent been back. He does have some nice rigs there though.
From this it sounds like you are thinking of buying a complete lower from one place and a complete upper from another and calling that "building". All you are doing in that case is slapping one on top of the other and pushing two pins, and I can see how you wouldnt save much, someone else is...
Come to the shoot on Oct 1st. There will be lots of AR's in different configurations and people are friendly about letting you shoot them
Here is me shooting my RRA entry tactical at sherburne
http://img.photobucket.com/albums/v664/rjszurgot/DSC00194.jpg
Stag lowers are top notch. The deer head I could do without, but the quality makes is worth it, and you can get them cheap. If I were to have one AR, It would probably be a 16'' midlength with a collapsible stock.
But with so many options available for the AR, even that description leaves...