If that is a genuine St Michael tray then not only will it be before your time by approx 2000 years but it will be extremely valuable to many religions. St Michael the Archangel is mentioned in the New Testament where he led God's armies against Satanic forces in the 'Book of Revelation'. St Michael is usually depicted carrying a banner and scales whilst treading on a dragon. Your tray does not appear to show either dragons or banners so it is possibly not a early 5th or 6th century object. It may even be as late as some of the 13th century Byzantine Icons. Either way I think you should delay the sale to Big Rhonda until you have it's provenance checked by your local Jewish, Christian or Islamic expert.
Sssh ! I was hoping for a bargain ,you have now outed it as a genuine religious artifact possibly of great historical import.He probably thought it was just a big 70's looking thing.
