Can anyone tell me the best place to buy a zetec 1800 engine?

Where are you on the planet...
Ps ebay may not be the best bet see my previous posts

you'll want a pre 95 one to get through SVA without strict emissions test.

Plenty of scrap dealers will sell you a low mileage one with some sort of warranty.

these people may have what you want

http://www.intapart.com/