I've got a Hepco rack that the prior owner of my Baghira installed. It is made of steel and seems to be very nicely built. I have a small topbox bolted to mine, but I imagine that a duffle bag or similar could also be made to work with it. $140 is a little steep for a rack, but I'd say this is worth it - provided you can actually get one.
Oh, keep in mind that this rack does replace the passenger grab rails, if that means anything to you.
Here's a picture: