it's quite simpel
X11 chassis stock = graphite
X11 chassis option = plastic
X10 chassis stock = graphite
X10 chasis option = extra light graphite (doesn't exist anymore I think)
XRS chassis = plastic
Your cheapest options are the 3 at the end
My friend who still has an XRS chassis is on holiday so can't contact him at the moment.
+I don't know it what condition it is. He bought my previous XRS so he will have loads of parts AND X10 parts. But I don't know how expensive it is to send to the other side of the world....