What's the price of fame for Hollywood starlet Sandra Bullock? On the upside, she's signed to do John Grisham's A Time to Kill for a thrilling $6 million. On the downside, Bullock can't just dance the night away anymore. Once an anonymous hoofer at an L.A. Cuban hot spot, now Bullock needs her handlers to work overtime to keep the club a secret from her fans. According to her spokeswoman, it's the only time the actress can check fame at the door: ''She doesn't get hassled there. Nobody cares who she is and she can just concentrate on dancing.'' In fact, some say Bullock is becoming a regular Tony Manero. Says one of the club's owners: ''She's one of our best.''