Depends on the AR’s in question. If you’re going to sacrifice somewhere don’t do it with your barrel or with critical QC testing.

You want your barrel to be 4150 CMV with either a Nitrided/QPQ/Melonite or chromed bore and most ideally, Cold Hammer Forged.

Some less expensive guns have 4140 barrels with plain phosphate coating. That’s suboptimal, you could see reduced barrel life and it’s more susceptible to corroding.

For $500 you should at least be able to build a gun with a 4150 Nitrided barrel which is mostly as good as anything else on accuracy and service life.

The next place corners can get cut is on testing and inspection. A lot of the guns at around $500 are not high pressure tested or Magnetic Particle inspected but some are. Be selective in looking for those two features with your budget build.

Assuming you were selective and found/built a $500 gun using parts that are MP/HP tested (BCG and Barrel) and your barrel is at least a 4150 CMV Nitrided barrel, I would expect comparable performance to a much more expensive rifle.