I found a page on the internet from 2003 where this plate apparantly was up for sale (doesn't appear that it sold) for between 70 and 90 pounds (UK). You view the information here:
Decorative Arts. It's #253.
Based upon that - if it's relatively accurate - your piece would be worth between $140 to $185 USD in 2003. Of course this would depend upon condition and present market value.
If I were you, I would register and check at Sotheby's. I have checked into the value of several pieces that I own there and they have been most helpful!
If you find out a present day value from a legitimate source, I would love to hear the results. : )
Hugs, Didi