Well, while typically you get what you pay for with glass, there are a few exceptions. I will let some others chime in here, I have no first hand experience with them, I have an issue where once I start shopping, my wife starts crying.
As far as the Mega barrel, a good friend of mine and the forum, had recommended one to me, saying he had shot someone's 18" to 600 with sub moa results. That's all I have, but it's something.