For a 16" mil-spec middy (seems to be the go-to for many), build it for that price.
Stripped Lower: $150 (give or take $50)
PSA LPK w/ MOE grip & stock: $120
PSA barreled upper, when on sale (often): $280
Quality M16 BCG + BCM Gunfighter CH: $190
Magpul rear MBUS + MOE handguard: $80
Vortex Strikefire Red/Green Dot sight: $150
Magpul P-Mags (2): $30
I've now spent all your money, but your rifle is complete. Heck, you even got a highly functional optic to mount atop your gun. And for what I'm after (your preferences may differ), that's a solid rifle that should run like a top. All you need after that is ammo, maybe a sling, and eventually a tacticool rifle case and even more mags to justify all those velcro pockets.
For builds on a budget, do look up JoeBob's
, and AIM
. They all get high marks for quality, service, and extremely fair pricing.