$5500
They would want to be 30 year old NOS for that, even then they'd be expensive.
I paid $2400 for Kawasaki pipes ....maybe 3 years ago though, Sydney City Motorcycles-Kawasaki. I think if you look about you'll still find 'em for around that price.
At the time Z-Power were $3000. Only difference with the current genuine pipes is they are lighter and no longer have the little cover ring between header/silencer that they did 30 years ago...just a silver frost paint ring.