Ok, here is one recipe for building a sub MOA AR for under $1000.
First, spend your money on your barrel. Nothing is nearly as important as your barrel.
Secondly, a good trigger.
Third, good optics.
Just about everything else is negotiable. Such as hand guards, never seen a full floating hand guard that was $200 make ANYONE shoot better. That being said, it should be a full floater, but you don't have to break the bank.
Billet uppers and lowers are nice, but you can get a forged set to shoot just fine with a good barrel.
Grips make a rifle nicer, but again, they don't cause you to shoot better or worse. Same with stocks.
As Hellgate said, it's all useless without good ammunition. Throwing mil surplus JUNK downrange will do great at making noise and holes in the dirt, but that's about it.
And as Bob said, a bit of know how goes a long way. If you know how it works you can build quite a rifle for a fair amount of money. Some guys just chase the demon by throwing money at it.