You can sign up on the CdeS website to become a friend, then you get the very occasional email from them, and a discount off your ticket. The other way is to go to the box office half an hour before the show starts, I believe they do cheap tickets then.
We booked via the friends and got front row side atage seats, astonishing. Mrs Stoat is an old curmugeon, shesaid she only glanced at her watch once during the performance and was amazed an hour had gone by.