PS:
A cheap color laser printer with duplex capability that supports PostScript
natively is the Lexmark CS310dn. (It sells for less than 115 € around here.)
Just be warned that I HAVE NEVER TRIED IT, I only had a very quick glance at
the specs for you. There might be a reason why it is so cheap. I recommend
doing some research on your own before buying this or any other printer.
Kevin Kofler