Building a single rifle for many purposes is a futile attempt. However, based on your specific needs, it's pretty simple. You set a BIG budget and I doubt if you really need that much. But, thinking on BIG budgets, this is what I would do.
Option #1
Usually, building an AR from a stripped receiver and bare components is the way to go. You get to choose exactly what parts and accessories you want and it's perfectly designed for your needs. This will cost more than an off-the-shelf AR, but it's what you want. However, this is not for the 1st time builder. Primary reason is that most "don't" know what they need or want. You spend stupid money on a build, then spend more to "fine tune" the build to you actual needs.
Option #2
So, most just buy a standard AR-15, shoot it, figure out what they need, then buy the upgrades. At the end, you will pay about the same, more, or less than option #1.
Personally, I like option #2, especially when you can get a great AR for less than buying it off-the-shelf. This is where
DSArms comes into the picture.
DSArms offer a complete AR-15 in the M4 configuration called DZA ZM4 Flat Top Carbine
#ZM4CV1RA4 for
$775.
- 16" Nitride Treated M4 Barrel
- 1:9 Twist Rate
- Forged Front Sight Base with Bayonet Lug
- 5.56 NATO Chamber
- M4 Handguards with Heat Shield
- A2 Birdcage Flash Hider
- A2 Pistol Grip
- 6 Position Collapsible M4 stock
- 7075T6 Alloy A3 Upper Receiver
- Includes 30 Round Magazine, Owners Manual, Hard Case
- Manufactured by DSA - All Parts U.S. Made!
Also through DSArms, you can buy the Field Stripped Components and save a bunch of money, AND get a complete rifle. Or, get an upgraded rifle for about the same money.

Model ZM4
Complete Lower Receiver With Mil-Spec Stock Assembly (includes buffer and spring) -
#ZM4RCAR-A $200.00

ZM4/AR15 Semi Auto, Complete
Bolt Group Assembly with NP3 finish -
#ZM485018509NP3-A $160.00
Gas Key Installed, Carrier Chrome Plated Internally (this is an upgrade from standard and will be easier to clean)

ZM4/AR15 alloy
Charging Handle complete with standard latch -
#ZM48517-A $14.00
Made from a 7075T6 Forging.

DSA ZM4 A3 Upper Receiver, 16" Barrel; M4 HG, Parked Chrome Lined -
#ZM4CBUM4PARKCL $300.00
- Forged 7075T6 A3 Flattop Upper Receiver
- Forged Front Sight Base with Bayonet Lug
- A2 Flash Hider
-16 Inch 5.56mm NATO
Chrome Lined 1:7 Twist ZM-4 Barrel (this is an upgrade. Makes easier cleaning, and allows for heavier bullets)
- M4 Style Handguards
- Aluminum Delta Ring
- M4 Style Feed Ramps
- Manufactured by DSA - All Parts U.S. Made!
Do the math: $200+$160+$14+$300=$674.00
Add your choice of magazine. I like the Magpul Pmag. A 30rnd mag is $15.00. A 20rnd mag is $14.00.
Add your choice of a case. I like soft cases with pockets for magazines. These can be had for $20.00
This brings the total to: $709.00
Need an owner's manual? Hell, download it free from the millions of resources on the
world wide web. It doesn't matter which manufacturer's manual you find. An AR-15 is an AR-15. Or, call DSArms and they will send it out for $6.00.
With these several components, you will end up with a BETTER rifle than the DSArms rifle shown above, and save some money.
I've built 6 of these rifles in the past 2 years for myself, friends, and family. Built is a strong word. It's more like I reassembled it. When you field strip an AR for cleaning, you'll end up with these 5 basic components anyways. Complete upper, complete lower, bolt carrier group, charging handle, and magazine. It's the same thing.
Every rifle I "reassembled" will shoot 1" groups @ 100 yards all day long with a quality 16x scope.
That'll leave you just under $800 to upgrade or add sights/optics.
Optics
For a 100yd rapid engagement rifle, I would suggest a low power variable scope and/or something with a "dot". I really like the Nikon
For a electronic dot, I would opt for the
Trijicon RMR dual illuminated dot. It has a fiber optic illuminator as well as a tritium insert. No batteries needed... ever. A super fine choice for a 45 degree mount for rapid upclose engagement. Pricy at
$550.00, but well worth it at the end. I HATE when I freakin forget to change my battery out because they die FAST in our Arizona heat.
For a variable scope, I REALLY like
Nikon M-223 scope in 2-8x power. It's also bullet drop compensated from 100-600 yards, when using a 55gr polymer tip or FMJ bullet. You have your choice of a knob that's marked from 0-600 yards in 50yd increments, or a BDC reticle with 6 circles that are marked for 100-600yards. A steal of a deal for
$330.00
Ok, maybe the Trijicon was a bit over the top. It could be easily replaced with the
Burris Fastfire III for
$250.00.
That'll leave you extra cash for an off-set scope mount and the 45degree mount for the red dot, a nice sling system,and a about 300 rounds of quality ammo.
Anything more than that is just bells & whistles. Feel the need to put more $$$ into it? You can opt for a barrel that has flutes to reduce barrel weight. Not a bad option for a $5.00 bucks more.
Yup. $5.00. Also from DSArms. You'll have to sacrifice the chromed lined barrel for a chrome moly barrel. Just clean the barrel a little more often... like once a month. :)
Seriously. You should clean it after every session, regardless of the type of barrel.
Think you want to squeeze EVERY bit of accuracy out of that 16" barrel? No problem. Replace that forend with a
YMH skeletonized free-float forend for around
$120.00. It'll add 10.6oz to the weight, but you'll be saving weight by buying the fluted barrel.
Hey, if weight was a concern, you could also opt for a carbon fiber forend. Expect to spend $300+ for a decent one.
PRI offers them for
$320. they're probably the best and weighs in at 8oz. without the rails. Install all 4 rails, then the weight goes up to 18oz.
Alexander Arms makes one, not in carbon fiber, but in G10 composite. Also very light weight and is $165. Accessory rails are $25 each. Weight is good at only 8oz until you add the rails. Then, you're at the same weight as the PRI, but spent less cash.
Clark Custom makes a standard carbon fiber tube. It's only 6oz, which is good. Comes with sling stud pre-installed, which is fantastic. Only $100, which is nice, but...I don't like them. It's pretty much a permanent install. Once on, you can't take it off without breaking the darn thing.
To each his own, my friend. Good luck on your build. Let me know if I can help you along. I have all the tools necessary.