Decent? Your price range is pretty low, but if it were me, I'd look into the SWFA's when they go on sale. Like wareagle suggested. Other than that, you have other options. One is made specifically for the AR by burris. It is called the MSR (Modern Sporting Rifle). I've ran them, but much prefer a step up to the Burris AR556 and 762 rifle scopes. Glass is much better on those and they are around $400.00. Anyway, the MSR works. Glass is about equal to the Leupold VX2 riflescopes. They have a good ballistic reticle, much like the old burris ballistic plex. Here are a few pics of that scope:
With that being said, I use the MSR scope on my 223 bolt gun and some of my rimfires.
I've used it on a couple AR's and they work, but like I said earlier, I prefer the AR556 and AR762 over the MSR. But the OP has a low price requirement.
I don't know what power range you are looking for, but these scopes can be had in 3-9x40 and 4.5-14x42