As to cost, it will greatly depend on the brand and quality of the parts you buy. The best costs more. Expect the price to come in around $600 minimum. You can actually buy a basic AR-15 in 5.56/.223 for less than you can build one as there are also necessary tools to buy that add to the cost.
Amazon.com offers several how to books that walk you through building your own AR-15. Your biggest hurdle will be the legality of the project, as I'm not sure if NY has an "assault weapons" ban. Be very careful here because you can turn yourself into a felon by doing something as simple as installing the wrong type of barrel. As for cost, it varies quite a bit. You can assemble a rifle that will go bang for less than 1000 bucks but you will probably have to cut some corners. the 1200 dollar range will allow you to build a good gun that is reliable.
As for tutorials, as others mentioned YouTube has videos covering everything from start to finish.
Now, as for cost and the build itself. I would strongly suggest that if you haven't owned an AR before that you buy a complete factory gun as your first. There are a few really decent rifles made by well known manufacturers that would be a great starting point for you to learn the platform and also you can modify and add parts to that rifle as you figure out what you like and don't like. There is much much more to building a rifle than just throwing a bunch of parts together, and in my eyes buying a complete lower and slapping a complete upper on it is not a build.
If you really are dead set on building a gun piece by piece then I would say you have a ton of research to do before you start. Cost wise you can spend anywhere from as low as $500-$700 on an entry level cheap gun with lower end parts, or you can spend several thousands putting together a high quality rifle. My last build I was at $2450 without the optic, and that was catching some stuff on sale too. So it's really up to you and what kind of rifle you want.
Going back to a complete rifle, I would really recommend you go this route. Ruger AR556, Smoth and Wesson Sport 2 are two great entry level guns that will serve you well as a learning tool. You can mod them as much as you want but the core of the gun will be put together by a major company so you don't have to worry about issues with random parts not working well together.
If you can spend a little more check out the OEM guns by Colt and Aero Precision. These are guns that come without hand guards, stocks, etc so you can pick whichever route you want to go. You can mount up a 15" free float rail and go with a modern look, or you can stick with something more basic like a Magpul handguard and fixed front sight. That may be a better option for you and the Colt and Aero are a good mid range gun that are going to perform better than the entry level Ruger and Smith Sport.
Just some stuff to think about. If you really are dead set on building just don't do what a lot of people do and throw a bunch of random parts they got on sale together. Do your research and buy quality stuff that is known to work well together.
You will need to find a non threaded non bayo luged barrel ..And most likly if you run it no pistol grip will need ambi controls and larger ones to run it ok ..And to find a self pistol grip or a FR15 stock which again
In a free state you can build a AR for under 500 bucks ..Like 300 for the upper and LPK and 50 bucks for the lower ..But in NY state
A forum community dedicated to defensive firearm owners and enthusiasts. Come join the discussion about everyday carry, optics, holsters, gunsmithing, styles, reviews, accessories, classifieds, and more!