There is no money to be saved by buying the cheapest AR now, and up-grading it later.
Get the most of what you want & can afford on a quality AR to begin with.
Then you won't be throwing away several hundred bucks worth of cheap barrels, sights, stocks, rails, etc., on down the road.
After which, you will still have a cheap AR with a Cheap AR brand name and no resale value after spending all that money to up-grade it.
rc