I'm interested in getting one. I wish that fixed buttstocks and 20" barrels were more common, they are quite a bit more expensive. Because of it and my limited budget, I've decided to get a standard 16". From my shopping around, I've found that they can be completely built for under $500. I figure that's a good entry level price.
Take my word for it (because I've done it) - building your own is no cheaper than buying one off the shelf, and is more often than not, more expensive. The ONLY reason one should build an AR himself is to build a BETTER rifle than you can buy off the shelf.
Cookie-cutter guns from the likes of S&W, Colt, RRA, and others are comprised of a 16-inch 1:9 barrel with a carbine-length gas system, an A2 flash hider, a semi-auto BCG, A2 front sight post, standard trigger, and the cheapest value furniture they can pass off to the masses, and all for the low low price of $700-1000 - with NO extras (magazines - I have 21 so far).
If you're going to build one, you want to build a BETTER rifle, meaning better components, which means more expensive components. If you're patient, and find really good deals, you might be able to squeak by for a total cash outlay of under $1500, and we're not even talking about the cost of tools you'll have to buy, which will vary according to what parts you're buying for your rifle.
Next, you gotta talk about optics. Want a red dot? How about a regular scope? Decent mounts for a regular scope STARTS at about $80. Mounts for red dots are $100 and up.
Finally, resale value on custom-made guns is absolutely abysmal. Most of the time, people that are knowledgeable wouldn't touch a used home-made AR (probably built by a mall ninja) with a 10-foot pole.
The point I'm trying to make is that building your own AR is more expensive than a lot of people consider, and there will likely be additional expenditures that are not on most people's lists. Finally, it's unlikely that you'll be able to recoup your money if you ever try to sell it.
For what it's worth, my home-made rifle cost me about $1200 to complete (not counting shipping and parts do-overs*). If you add all that up, we're probably talking in the neighborhood of $1700 - WITHOUT optics.
Here's my web page that describes the parts I put in it:
http://www.paddedwall.org/guns/rifles.aspx
It's the first rifle shown on the page.
* A "parts do-over is where I had to order parts a second time, or when I changed my mind about configuration, or to replace a part I managed to somehow booger-up.
