Do a little research and build your own, IMO...once you realize all the things that you will want to change from most factory completes you will only be saving $$$by not paying for components you will replace anyway - a few examples include trigger, forearm/handguard, flash hider, stock, sights or optics, etc and that's just the beginning.. It is surprisingly simple to build and requires few special tools ....just built my first with quality components and even bought the tools I needed (roll pin punch set, upper receiver vise block, stock wrench and a couple others) and all said and done total, I'm in less than $800 with the exact rifle I wanted. Most of the tools you need are inexpensive or can be borrowed from auto zone or maybe even benevolent guys here or your own buddies.
Check out ar15.com for lots of helpful tutorials, etc...I really enjoyed building my own and - for me, anyway. - I feel better knowing where all my components came from...