Alright, if you want a jump on me in this thread, keep these links open- In stock lower receiver thread
Lots of BS to shift through, but if you have any questions, ask on here. Basically be on the lookout for any stripped lower for under $150, or complete lower for less than $400. Usually they will say if they are metal or polymer. In Stock Uppers
This link has been a lifesaver. Order from Midway, PK firearms, Bravo Company if you can. The ones from Midway and PK usually come with BCGs and charging handles, but most of Bravo Company's does not, so you will have to wait for those to be in stock.
You can look on Palmetto State right now and get a lower parts kit for your future stripped upper for $200, or you can wait for their classic one, that has standard MOE furniture instead of MAGPUL, for less.