My advice is to buy the nicest AR you can afford. There are many who will tell you entry-level ARs are plenty good, and that home-built rifles from parts kits are the way to go. That may be true for some, but it has never worked out that way for me. I have owned a half dozen or more ARs over the last 10-12 years. I started out going the cheapest route, and my first two ARs were assembled from kits on stripped lowers. They were mostly OK for casual shooting, but they were sometimes finicky about ammo and were never completely reliable. Ultimately, both guns suffered serious parts failures when I pushed them hard at a two-day Appleseed shoot. That led me to get rid of my entry-level rifles and invest in something serious. I ended up with a complete BCM upper and LMT lower. That rifle has been a complete joy. Even when pushed hard, it has NEVER given me trouble. So, as I said, just get something nice to begin with.
More recently, I bought a Colt 6920 in their "OEM" configuration. As someone has already mentioned above, these are mostly complete Colt M4 carbines lacking only a handguard, stock, rear sight, and triggerguard. With shipping and an FFL fee, mine still cost under $750. I bought an M4 stock and double-shielded handguard from BCM for under $50. I already had a rear sight and triggerguard, but these can also be picked up for little money. Right now, I have about $800 in a brand-new Colt. When entry-level parts kits guns can cost upwards of $600, the OEM Colt 6920 is hard to beat.