Sounds like a fair price as far as Lexus dealers go. Like Maneesh, worth finding an independent that you can use (not that they would've got an exhaust bit any cheaper mind you). As an example, the rear crank oil seal had gone on mine. Lexus quoted £940 for the job, The independent I always use for the MOT was £250. The torque convertor seal had also gone so the total bill came to £313. A bit of a saving