Brands to stay away from:
Come on down to the AR forum and we'll answer all your build questions, and probably cost you some money with new idea for additional builds.
Here's a recent thread on inexpensive AR buildsInexpensive AR builds
Here's a few guidelines.
Your two most important parts or the barrel and BCG, and some will argue followed by the trigger. Spend your money here and save on the commodity parts.
So long as your lower is dimensionally correct, it'll work fine. This is a good place to save money. Uppers receivers are a little more critical, for an accuracy build, they tighter they fit to the barrel extension the better. Beyond that, dimensionally correct is good enough. so most people save money here.
Triggers, ALG is nice for the money, I like a good Geissele Trigger.
Lower parts kits. Any of the mid tier and up kits, starting as PSA CMMG etc. and up are good, just don't buy Anderson for the LPK, they are know for out of spec springs and pins.
Just about everything else is personal preference.