The term 'Expensive String' can be broken down into two crossword solutions: Pearls (6 letters) and AMATI (5 letters). Pearls are a type of gemstone that is formed inside of certain mollusks, such as oysters. They are highly valued for their beauty and rarity, and have been used in jewelry for centuries. AMATI is the name of an Italian family of violin makers who were active from the 16th to the 18th centuries. Their instruments are highly sought after by musicians and collectors alike, and are considered some of the finest examples of stringed instruments ever made.