Well, you can get a complete unit. The choices of factory made are Rock River Arms (RRA), American Spirit Arms (ASA, or Olympic Arms.
They typically run 600-800 completed (depending on config).
Building price outlook:
Lower (Eagle Arms or Mega) about 95.00
Butt kit- 50.00 avg
parts kit-50.00
Total lower- 195.00
RRA (basic 9 upper) 450
adapter block 150
You spend about the same, but if you are strapped for cash.... parting it isn't as hard on the wallet.
Edit- for got to address the home protection part.
Well, reliability is based on the parts. Example, the mag. I would get some mag and load them w/ different ammo and "unload". Use the ones that do not cause ANY type of malfuction.
My 9mm? I have some mags that have not yet failed me. I would use those. We are talkinga bout 30 rounds unloaded as fast as I can pull the trigger.