How long can you wait? Two days? Buy now. Two months? Track the price and see what happens.
As a wealthy Renaissance merchant, acquire mines and transportation, hire artisans and woo the nobility. Create the most fantastic jewelry to become the best-known merchant of them all! Acquire precious stones to trade them for development cards. Use development cards to acquire more gem stones. Use your gems and gold to create the most fantastic jewelry, and appeal to the nobles to gain the prestige you need to win.