Re: olympic
If you spend in a hurry on this you'll regret it. The way the economy is, you can't assume that you'll be able to re-sell without taking a a big loss if it turns out you don't like it, or want something else later.
$200 seems a bit low for a "decent" scope, unless you're talking a real basic fixed power with a plain reticle. For comparison, you can pick up a new Super Sniper w/ mount for $300, and have something that is perfectly functional and durable and not a waste of money by any means. I'm sure there are a ton of "what is the highest quality scope I can get for $300" threads over in the optics section.
A red dot is a different matter, but for the $200 you'd be much better off putting that into the rifle rather than into a red dot in that range. $1000 will get you a top quality brand new AR-15; $800, and you either need to take your time and find a great deal, or cut corners.
If you're looking to cut corners on the budget and you can't assemble it yourself, your best bet is probably to keep an eye out on the for-sale forums. A lot of guys are unloading new and like new uppers for pretty cheap. It's not hard to find GOOD uppers, like new in box, for the same price or less than many CHEAP uppers are selling for, retail.
You might do something like this -
Find a good deal on a new or like new complete upper from a good company - $500
Get a lower, just about any will do - $250
That leaves $250 ... you can probably squeeze a basic, but good quality scope in there. Don't try to buy bells and whistles that you just can't afford (variable power, illumination, etc).
There really has never been a better time to buy or build an AR, you just have to make good decisions. It would not be unreasonable to be able to get a lower in whatever brand you want, an upper from some place like Bravo Company, Colt, or LMT, and a Super Sniper w/ mount for $1050 (minus shipping).