Wtb 16" AR upper receiver

[Atomic Donut]

Looking for a 16" or a 14.5" upper chambered in 5.56. looking for a BCM, S&W m&p, or Stag upper, but will consider any brand. Trying to keep budget around 400ish so if you got anything please let me know. Seeing what is out there before I buy one at the Oct 24th Vallejo gun show. Thanks

looking for Flat top style A3 or A4 and 1/7 or 1/9 barrel.