Stick is referring to the Federal Assault Weapons ban that went into effect September 13, 1994, and expired Spetember 13, 2004. The ban included restricting certain features of "assault weapons" manufactured after the Sep 13 1994 active date such as flash hiders, collapsable stocks, and high-capacity ammunition feeding devices (read: high-cap magazines). Even though the Federal AWB expired, some states have their own AWB's that are similar in design to the Federal version. New York is one of those states.
I don't know the specifics of NY's AWB, but many folks have opted to purchase receivers that were manufactured prior to Sep 1994, thus making them "pre-ban" and not subject to the same restrictions covered by an AWB. These preban receivers carried a higher market value, but allowed the owner to add the "evil" features.
You will have to check your state laws as to what you can and can't have. As far as obtaining an AR variant, they can be had in your price range. I would suggest looking at the Equipment Exchange portion of this site, as there are alot of good deals to be had.
As far as AR configurations, it basically boils down to the type of shooting you are going to be doing versus the look you want. The AR has become quite the modular system. The basic question you must ask yourself is "rifle or carbine....?" From there, it can be narrowed down even further, from fixed or foldable sights, addition of railed handguards, addition of optics, bipods, and aftermarket/custom grips and stocks. You are only really limited by your budget and what state law allows.