Tonykay 02-05-11: Used units on Audiogon are safe bets. Stax headphones are hard to damage-I've been using mine for about 20 years and they still sound GREAT!Ditto!
If you want to consider a used pair of Stax's, you should be aware that original Stax replacement earpads can be obtained from Audiocubes2.
The earpads are supplied together with a replacement for the piece of foam that covers the electrostatic element. A couple of years ago I replaced the pads and the foam on my mid-1980's Stax Lambda Pro's, because the foam was disintegrating. They continue to work as new, after 26 years.
Regards,
-- Al