I got one for $639 and the second one for $598. ARs are not going to get any cheaper. I'd say you got a good score. Congrats!

I've done allot of research on ARs for my winter project. The absolute cheapest AR you can build will cost $515, (if you don't have a buddy giving you some freebees). That is no melonite, chrome, stainless barrel (chromoly), no warranty, and no resale value. However, you will have the fancy dust cover if you plan on rolling in the mud.
$80 stripped receiver
$80 LPK
$90 BCG & charging handle
$200 upper (16" carbine, all others are more $)
$15 magazine
$50 rear sight (Magpul flip up, UTG carry handle only $40)