Prince went to Michael White’s Soho restaurant Costata Friday night, but couldn’t pay the bill because he forgot cash. Spies said his Purpleness, who performed at City Winery Thursday night to a full house, rolled in with “an afro and a pimp cane.” But while his guest had pasta, scallops, veggies and fries, Prince didn’t eat. “He simply drank royal blushes,” a spy said. He handed the check to his security guard, who then called the restaurant manager over, saying somehow Prince’s management forgot to give them cash. Sources said the guard left his number and said he would be in touch the next day to pay up. No word yet if that happened.