Buy a good LPK (lower parts kit) and start thinking about what kind of AR you want to end up with. The Daniel Defense LPK (about $90) is pretty sought after, but it's also awful hard to find. I think Spikes offers some good LPKs for very good prices through JoeBob's
. But those are both combat type setups, which may or may not be what you're after.
Figure out what barrel, handguard, and twist rate you want. Don't let anyone tell you that you need a 1:7 twist
. It might in fact be ideal for you, and it also might not. 1:7 has benefits. But 1:8 is super versatile. And 1:9 will handle about 95+% of the stuff that most AR owners run through their guns.
The point is, do your own research and figure out what upper configuration suits your needs. Same for the trigger, especially if your goal is a target/varmint gun.
Find a barrel, bolt, optics, and trigger that suit your needs...probably in that order. But the latter two get a bit of a priority boost if your goal is to slow-fire super tight groups.