I guess I could answer that more specifically. I'll go as low as possible in price, preferably with someone else paying me to take stuff from them. That'd be great.
But I'd consider a "budget build" in terms of how low in quality of parts am I willing to go.
Upper and lower receivers.... Whatever is cheapest, although I prefer to not have some ridiculous logo on the side of my lower.
Stock and grip.... You can get a set of Magpul for about $35 if you shop around and I guess that's cheap enough. I'm a sissy so I do prefer to have the little gap by the trigger guard filled in with the grip or trigger guard itself.
Receiver extension / buffer / spring.... Whatever milspec sized extension is cheapest, I'm not terribly concerned with the actual aluminum used but I would like the milspec size so my stocks are interchangeable. I'll slum a carbine buffer if that's what's available but that's something that I usually get to suit the gun. I much prefer Springco buffer springs as I can get them for less than $20 and they'll never wear out. I hate doing any sort of maintenance on my guns so that might not be as big of an issue for someone else.
Handguard / Rail.... Again, MOE stuff can be had cheap if not free from a buddy, so that's about as cheap as I'll go.
Barrel.... I'm not buying a barrel that I don't know anything about from
www.bobsbarrelemporiumandsnowconestand.com. Decent FN barrels can be had from PSA or I'd get a Rainier branded barrel. For a budget build I'd probably try a Faxon barre.
You can get a BCG from a known manufacturer for $140ish and I won't budge on the quality of that. But again, the first thing I'd do is replace the extractor spring with one from Springco.
LPK & Trigger.... $65ish from a known manufacturer of good stuff. Although I'm a huge trigger snob and would just wait until I had an extra $50 for an ALG trigger.
So I'd guess that my budget build would run about...
Lower / Upper $120
Furniture $60
LPK / Trigger $80ish?
Receiver extension / Spring / Buffer $65
Barrel / Gas block / Gas tube $185
BCG $150
So $665 for a gun without sights.
I'm sure it could be done cheaper if you waited for Thanksgiving sales at PSA and bought one of their kits. And if it had one of their FN barrels and I could replace the springs and it didn't have a PTAC LPK I'd do it.
Well, I'd do it if I wanted a budget AR. But I don't have a need for another AR just for the sake of having one around so I really wouldn't do that. I'd rather keep saving and get one that I would really use.
