Diamind Bikini $ 30 million In 2006, super model Molly Sims wore a diamond bikini in a Sports Illustrated Swimsuit Issue. This was claimed to be the most expensive bikini in the world. The fact is, it is also one of the most expensive jewelry pieces to date, with a price tag of $30 million. The bikini has over 150-carat diamonds all set in platinum. It was designed by Susan Rosen and Steinmetz Diamonds.