Thanks! I think I charged her a couple hundred, maybe $250, but I do remember, she didn't bat an eye at the cost - apparently, she'd priced them outside, as well. And, YES, they make a special liner/stiffener for up at the top - I think it's about 4-5 inches wide, and it's stiff, but doesn't effect the drape of the drapes.
I can't think of any reason not to use linen, unless you're worried about how thin it might be. Maybe you could stabilize it with lightweight fusible interfacing? I don't know, but I used that quilter's cotton (I'm pretty sure it was from Bonnie & Camille) without issue. But I did serge all the edges..all of 'em. Good luck!