$120 - 16" CMMG Barrel:
* 5.56 / .223
* 1:7 twist
* Carbine length gas
* M4 profile
* Polished M4 feed ramps
* 1/2" - 28 threads
* 0.750" gas block diameter
* https://cmmg.com/barrel-sub-assm-16-1-m4-4140cm-sbn-5-56mm
$50 - Aero Precision adjustable gas block and gas tube. Like new. Only 40 rounds through it.
https://www.opticsplanet.com/aero-precision-adjustable-low-profile-gas-block-w-aero-logo.html?_iv_code=29D-RGB-AGB1-APRH101676C
$140 - Daniel Defense Omega Rail 7.0
* Very good condition
https://www.opticsplanet.com/daniel-defense-omega-rail-7-0-carbine-dd-10001.html?_iv_code=DDD-HZ-OMGRL-DD-10001
$80 - Folding front sight / gas block combo.