HI. I recently found an antique ring EGL certified Old mine cut square...2.552 cts SI11, I, 9.32X8.82X 3.95mm. How much is too much?? It has two small side stones on each side and is set in platinum. Dealer said it is from 1910. I love it but was told it is a good buy at $20,000. HElp...please.