Colin, my nearest Lexus dealer wanted to charge me £1,135 for a timing belt change, which included the belt, tensioner pulley, hydraulic tensioner, idler pulley, and waterpump. I politely declined. I ended up going to an independent garage who specialises in Toyoya /Lexus. I had it all done, including new coolant, for £625. So, I would say your quote was a very good one. Make sure it includes replacing ALL of the above.