There are two things to consider when purchasing/building an AR and you are budget minded.
1. Does it fire when you pull the trigger
2. Is this rifle for your job, 3-gun matches, or for plinking.
If it is for a hobby than any brand AR will be fine - you don't need a high dollar LaRue to plink, unless you want to.
If it is for 3-gun events, generally you are still fine with any brand. But this starts treading into the dollar vs. value argument
If it is for your job and your life depends on it, simply do your research and read reviews from other people in your field. Buy based on that.
Also, as silverado113 mentioned, assembling and re-selling is a gray area. And no one wants to be a test case for the ATF.
On one hand, if I sell one assembled rifle a month - does that constitute "main portion of business"?
On the other hand, the mere act of taking one already manufactured upper receiver and one already manufactured lower receiver and simply placing them together tags you yourself as a manufacturer per their definition.
Now how silly is that?
That is like saying you are a manufacturer of Lego's because you put existing pieces together. Or you manufactured a sandwhich by putting bread and meat together.
Did you know to refinish rifles like I do (regulated parts) I have to have a FFL? You read that correctly, applying a finish to a regulated part requires a FFL. Luckily for me, my local FFL has me on his payroll as a sub contractor so I can stay legal.
The whole ATF system is ridiculous.