You don't even have to spend $800 to get a decent carbine, which is the sickening part. Unless you want to be obnoxiously cheap, you can build a decent carbine for $650-$750.
Cav Arms Lower - $89 from dsgarms.com
G&R Lower Parts Kit - $65ish
Bravo Company Upper - take your pick - carbine or middy $385 + $145for BCG and CH
Decent BUIS - $60-$100
