Investors had reason to cheer last week. But the valuation on this drone stock remains sky high.I've been following military drone manufacturer AeroVironment (AVAV -2.32%) for a very long time -- ever since it was just a newborn babe of a defense stock after its 2007 initial public offering (IPO), in fact. And I have to tell you that, over all this time, I've never seen AeroVironment win a defense contract as big as the one that it won last Tuesday: $1 billion.Well, $990 million to be exact.The Aug. 27 edit ...