$800 is ambitious, the upper will likely bust that figure.
I looked into the ASA two years ago, but when LAR Grizzly had a blem sale for a standard stripped A3 upper at $60 shipped, I gave it up. My build still came in over $1K, in an alternate caliber, A1 stock and rifle handguards.
Mechanically, a build isn't difficult. If someone has changed a water pump on a car, they can build an AR. What is the real difficulty is finding balance in choosing the components. There's a lot of extreme use or high precision emphasis in parts, but the priorities get misplaced, and the gun becomes overpriced for it's performance.
Goes back to what it will be used for, ranges and target. How much lethal force needs to go how far? Once the caliber is chosen ( it's that open ended with the AR,) then you match that ballistic performance with rifling and barrel length. That determines the gas port location, which is really about 5-7 inches from the muzzle on most AR's. Carbine is the exception, and it's exactly that, with a definite set of disadvantages based on being milspec for a 14.5" barrel on a NFA legal 16" gun.
Get the barrel sorted out, and then everything else follows in a priority of what it can contribute to it's final use. 1) upper, 2) optic, 3) furniture, 4) trigger.
All too many get it backwards and buy a 2MOA milspec issue barrel, then add expensive stocks, a target trigger, a CQB four rail handguard, etc. What results is $1,500 worth of parts screwed to a $150 barrel (with M203 cuts on it.)
When you look at the progression of priority, it's barrel first, and bling last. What grip goes on it is something way down the list - after all, the rifle is held by the off hand and shoulder, the grip is just a trigger finger rest. It's not like a pistol, where the grip is the #1 contact point for control and accuracy, AR grips are much less important. Having the "wrong" one might cost someone a point or two in a high level three gun match, but it's arguable.
Which is exactly what may happen in discussing prioritizing the value of a specific gun part. People get money and ego invested in justification, and lots of what if? and some very speculative scenario building are trotted out. Most of the stuff that gets recommended is usually based on an extreme application. In reality, all the charging handles, modular grips, and special stocks are neither necessary or even on the SOPMOD list to be used in extreme applications. It's really just marketing and agendas.
Caliber, barrel, upper, optic, furniture, trigger. It's a descending order of importance, and getting it backwards just spends money for nothing.
