I don't know the economics well enough to give the best answer, but I can assure you that much cheaper, and entirely decent, running shorts can be found.
Bill Rodgers Sportswear *still* seems to have plenty of stuff for next to nothing, at least two years into a closeout:
http://www.shopfest.com/runners_sportswear/index.htm
Their shorts seem fine to me, and I'm recently reminded that Supplex (nylon) workout clothes (some of the shorts here) don't reek anywhere near as bad as polyester, which is what nearly everything is made from these days.
People seem to like Eastbay's cheap splits too, though I can't personally vouch for 'em. Check soark.com. I used to routinely find pretty good stuff (Nike, Brooks, etc) at my local Marshall's too.