A $200 class 3 permit is all you need here in TN, but it comes with strings attached that not everybody wants....plus, full auto gets expensive quickly.
Check out
www.ar15.com to learn more about the AR. I currently have an S&W M&P 15, and grew up on Colt SP1's. I love my M&P, but it is actually made by Stag arms....IMO Stag is probably the best bang for your buck. They also make a left handed model. Bushmaster, Rock River, GSE...there's a lot of good names. Also look at
www.gunsamerica.com before you buy so you know the market. You should be able to pick up a very nice AR for around $700 - $800. An M&P around $1,000 - $1,400 and an SP1 anywhere from $1,600 - $2,000+ Colt wrote the book and is hands down the most appreciable if investment is a consideration.
FWIW, my little brother's a Marine on his second tour in Iraq. They're using Fabrique National (FN) M16 M4's.... Made in US, and a very nice weapon, but I think it's an odd place to outsource....especially with Colt's current struggles. http://en.wikipedia.org/wiki/Colt's_Manufacturing_Company