ENGAGEMENT RINGS! please help 10points to bestanswer!?

so my fiance` got me an engagement ring, today is actually our 2 year mark together.. well. come to find out the ring turns my finger green. i knew it wasn't real, but it meant alot cause he loves me. he was in the marines, and he got medically discharged due to being hit with chemicals in the gulf war. he only makes about 2,000k a month. he wanted me to ask on here.. does anyone know of cheap engagement rings, that are REAL gold or silver that WONT TURN MY FINGER GREEN? it's okay if its cubic zirconia, but.. its been awhile and he wants me to be able to wear it on my finger. i've looked on Ebay, Amazon, and craigslist. we cant finance one because of his credit. please helP!