Re: first 308ar build
DPMS upper, A3? (low height) = 165 @ JSESurplus
Tactical Machining Lower = 250$ (got mine used for 170)
DPMS LPK = 60 @ JSESurplus
DPMS 308 BCG = Rainier or JSE, 200-220
Trigger = RRA 2 stage, Geisselle SSA? nonadjustable 120-180$
Handguards = Troy Extreme, DPMS SASS, DPMS 4 rail low 120-220$
Barrel = Rainier Select 16-18, Fulton 16/18 chrome lined = 259-309 (Rainier or Brownells)
Gas block = pick one (you'll need a gas tube and gas tube roll pin as well)
AR10 A2 stock set = 90$ at 762sass
If you want a carbine stock then milspec buffer tube, DPMS 308 buffer + spring, egg plate, lock ring, and magpul ACS stock JSESurplus = 180$ or so
Flash Hider/Muzzle brake = your choice I use YHM 28? it was 30bucks or so at JSESurplus
You will also need an action block and multi wrench thing, JSESurplus has them for 40 for block and 25 for wrench. Then get a vise at harbor freight if you don't have one. That's assuming you have screwdrivers, allen wrenches, torque wrench in you garage already.
This is in a nutshell what I just built for myself using fulton 16" stainless barrel. It is "sub moa" with the right ammo and when I do everything correctly. The only thing I'd change about mine is the barrel (It's too heavy for a 16") rainier select 16" half pound or more lighter.
If you want "better" parts the stuff I would substitute would be mega upper lower set (600 vs about 400 for TM and DPMS upper lower) and a custom barrel (figure 450-500) and magpul PRS stock if you need the adjustment (extra 220 bucks).
edit: if you're really anal about accuracy go with a custom barrel just keep in mind that the limiting factor is almost always the shooter not the rifle.