PWS makes some great buffer tubes with prices to match (CNC with integrated sling mounts and other features).
Really, you should be able to find a decent carbine or rifle length, milspec or commercial tube under fifty bucks from any of the major distributors of AR parts online (Brownells, Midway, CMMG, Aim Surplus, Larue, LMT, Rainier, etc.). Typical price is ~$20 without a spring or buffer, although the way things have changed after Hillary lost it might be around that now with a spring and buffer.
For the stock, anything Magpul.