Help me build my first AR

I've been lurking the subreddit for a few weeks and have finally steered away from buying a Springfield SAINT and looking to building a comparable firearm for a cheaper price (lots of people feel the SAINT is over-priced. I don't know enough to agree or disagree). It seems to have some solid specs/reviews for a starter AR. I've looked at the Ruger 556 and M&P Sport II and like both; only downside with those 2 is the Carbine length gas system.

But onto the point of the post; based off what I've read via lurking, this is what I'm looking for:

• AR will be used for home defense and range shooting

• Budget is <$800

• Must be mid-length gas system

• Must have M4 Feed Ramps

• Would prefer M-LOK or Keymod handguard

Is this do-able? And what should I be looking for as far as brands/pricing?

Thank you for your time and expertise in advance!