The Royal Court Theatre is drastically cutting ticket prices on August 31. Theatregoers can see Howard Korder's The Lights for just 75 pence. The reason? This will be the last performance at the Royal Court Theatre, at Sloane Square. The Royal Court is scheduled to undergo extensive refurbishment plans and is not expected to reopen until sometimes in 1998. As of September 12, the Ambassadors Theatre, located on West Street, will be known as the Royal Court Theatre Upstairs and will feature such plays as Harold Pinter's Ashes to Ahses and The Royal Court/Marks & Spencer Young Writers' Festival. The Duke of York's on St. Martin's Lane which currently house Alan Ayckbourn and Andrew Lloyd Webber's By Jeeves will be known as the Royal Court Theatre Downstairs -- as of October 10 -- and will feature Jez Butterworth's play Mojo and The Beauty Queen of Leenane.