My mother used to buy what you're looking for from QVC. They had, what were they called?, CZ stones in gold rings for $50-$75. Looked exactly like the real deal. Since its just an ornament, its just as good as the real deal, IMHO, but that's another issue.

Ah yes, they were called "Diamondique". This should be exactly what you want for your temporary ring. They have the ridiculous guady sizes, but also some that look like real diamond rings that an ordinary human would buy. Reputable company, extremely low prices due to very high volume.

Jim