I would strongly suggest that being a knowledgeable mechanic would go a lot further assembling the AR 15. And having done so, I can say you won't save any money doing it.
First, you get stuck buying all the parts at individual retail, nobody sells them for a penny over the quantity price they got for an order of 10,000. They are in business to make a profit, when you see "blem" prices they still aren't rock bottom. They add their overhead to move it thru the shelf into a box to ship. It's cheap, but it's far from their cost to hit the dock.
Assembling the AR is problematic. Too much of the internet reads the Armorer's instructions, which are geared to having 20 something non gun users with no engineering background fix a machine gun at their limited level of repair. At best, the instructions you can read are meant to keep that kid from screwing things up worse, and considering they can break bowling balls just having fun, an AR hasn't a chance.
The assembly stickies detail it - you can break off the trigger guard ears, pounding roll pins in with punches will net scars on misstrikes, the springs can get on the trigger backwards and the pins walk out because they aren't locked into place. The barrel nut if turned too far will strip the threads on the aluminum nose - that 80 pound torque figure isn't a goal, it's something to avoid so you don't ruin the upper.
A mechanic knows by experienced feel what the difference is from 30 to 80 pounds, and if the nut isn't aligning, they can "square" the nose a thousandth and it will. They do it assembling car parts or other mechanically fastened devices for a living.
The assembly line workers at Colt, FN, and others don't need or use armorer's tools or techniques to build AR's. In fact, it's the inside industry joke. When you have hundreds to do daily, fiddling with clevis pins or dialing in a torque wrench is a waste of time. There's a 50 foot pound envelope of being "right," and all it really amounts to is getting the gas tube past the serrations on the barrel nut to trap it from loosening.
It's not rocket science. It's mechanics, which explains in this day and age why so few understand how to assemble an AR. Nobody much does that anymore as a teen, and few have a father to step them thru it.
The fact that you can nearly assemble an AR 15 on the kitchen table should tell you something, tho - a team of engineers figured it out pretty well. No pressing the barrel into the receiver while simultaneously setting the headspace with the AR. It's much much simpler than that, and why you don't have to be a trained senior level gunsmith. Or engineer.
But, you better know your mechanical aptitude. At least Stark makes grips for when you don't.
