Stone's amfAR fundraiser brings out Robin Williams, Gael Garcia Bernal and others

Sharon Stone and Robin Williams kept the jokes coming at an AIDS charity dinner in Cannes – but also made sober comments about the deadly disease.

“There are now 14 million people with the illness,” Stone said at Thursday night’s fundraiser for the Foundation for AIDS Research (amfAR). “We can’t stop until we have a vaccine.”

At the auction at the Cinema Against AIDS dinner benefiting amfAR, Williams – who during cocktail hour walked around pretending to be part of the waitstaff – put in the winning bid of $40,000 for an Armani black-and-white cylindrical diamond necklace.

“I just bought a $40,000 coke vial,” he quipped.

Trying to spur bidding above $60,000 for a vacation package in the south of France, he joked, “One picture of Angelina Jolie’s baby and you can buy this.”

Later Williams jumped on stage to sing with Wyclef Jean, and then paid $80,000 for an impromptu performance by the singer-activist.

Stone also brought levity to the proceedings, telling guests, “Before the auction we have already made $2 million. But don’t think that means I’m not coming for your cash!” The dinner raised more than $4 million.

Other celebrity guests included Rosario Dawson and boyfriend Jason Lewis, Sofia Coppola, Duran Duran’s Nick Rhodes, Ziyi Zhang, Michelle Yeoh, Faye Dunaway, Samuel L. Jackson, Willem Dafoe and Petra Nemcova (who danced during Wyclef Jean’s performance and took pictures for several guests from her front-row seat).

Lance Armstrong was in the men’s room when he was called up to the podium to conduct an auction. To much laughter – and the sound system playing Queen’s “Bicycle Race” – Armstrong dashed to the stage.

Sarah Ferguson, the Duchess of York (“We’ve got a Duchess of York and some queens from Brooklyn,” cracked Williams) told PEOPLE she was “delighted” to do her part at the dinner and spoke of a recent trip to Africa, where a little girl whose parents had died of AIDS asked Ferguson if she liked her dress. “It’s heartbreaking,” she said.

Though he was there to show his support, Babel star Gael Garcia Bernal told PEOPLE he didn’t plan to bid on any of the auction items – because, after four days of interviews and “no more than two hours of sleep per night, I’m just surprised I haven’t fallen asleep yet.”