Jason,
If you want to take a leap into the rifle world (AR-15), look for a used rifle. Unless you really know what you want/need, you have to start with the basics. I recommend a Bushmaster, or Colt, "patrol carbine." This is typically a short-barrel model (16") with a collapsible stock. Just get one with a carry handle and iron (peep) sights, and learn how to shoot it. Good instruction cannot be stressed enough. When you get proficient with good old iron sights, you can move on to more complex optics, like red-dot sights. I know this may seem a little "Greek" to you, right now, but a little research will educate you quickly.
One of the biggest mistakes novice AR owners/shooters make is to get caught up in the whole "what all can I hang on my AR to make it look cool, like the movies?" trap. I've shot many thousands of rounds through AR-15s and M-16s with nothing more than iron peep sights, and they get the job done quite well! No amount of modern technology can replace learning basic shooting fundamentals and practice. The AR-15 is a really fun rifle to shoot; you can shoot it all day, and not have a sore shoulder! Very little recoil, but very powerful still. I taught a patrol rifle course for years, and carried one daily. It's a very capable rifle, and learning it properly is a lot of fun! Keep it simple, and you can find one pretty cheap.
