build or buy?
If you are willing to try something new, learn alot in the process, and save a few $$$'s, you can put one together yourself, either from a parts kit or buying a complete upper and complete lower. Check out Del-ton, J & T, PK Firearms, to name a few, for complete uppers and complete lowers. If you shop around, you could get into a complete firearm for under $700 easily, maybe even under $600.
The other way of course is to find a complete rifle or carbine, preassembled. This way, you also get the security of a warranty, even though most reputable brands will also provide warranties on parts, such as the complete uppers and lowers.
As for brands, that's like shopping for a vehicle. Everyone has a favorite, based on whatever. You can't go wrong with the major brands, Colt, Armalite, Bushmaster, Rock River Arms, DPMS, Stag, to name a few. Or if your wallet is bottomless, check out Les Baer, Wilson Combat, JP, etc.
Find your comfort zone $$$-wise, then check out the internet sites, like this one, to get ideas, and do some searching. Good luck on whatever you find.