depends on what you're after imo.. there are plenty of bits easily available in this country for building a zetec turbo and one could probably be done relatively cheaply.

I think turbocharging the duratec would probably cost a fair bit more due to one off bits and development, but I seem to remember people in the U.S. were already turboing these some time ago with very good results. speak to some engine builders you trust re this option imo.

as far as turbocharging a zetec goes, I'd say start with the ST170 engine and go from there. it has a much better head than the other zetecs