I have a radical arms 7.5in AR pistol upper. No problems with it as well. (I know its not finding the OP an affordable upper, but just wanted to also give my input on it)
Im using a Primary Arms 1-6x scope
$269+$60 for the mount + whatever shipping is.
Glass is decent, eye relief is "eh" and its heavy, 1-6x is really nice especially for the price.
I also have a Aimpoint Pro with a QD mount. Its excellent but my eyes suck so I need magnification but didn't...