I think you can get a set of custom CCW wheels in boxster fitment in that weight range in 17". Their 18x12 size weighs 21 lbs so I'm sure the 17x9/10 sizes will weigh much less. Around $2500 for a set.
If my digital bathroom scale is accurate and Tirerack is right in saying a Mich PS2 18x9 is 25lb, then a Fikse profil 5 18x9 is 17lb. The same scale says my stock twist wheels are in the low 20s although I was told they would be 30+.