Entertainment book voucher - Sealink Kangaroo Island Ferry Transfer

Hi guys, just ended up planning a trip to go to Kangaroo Island tomorrow for 3 days(8-10 Nov). Been planning a visit for a few months but kind of happened all of a sudden because of the timing of some approved annual leaves and missus' wish. I work rostered shifts and weekends so a change of date would not be an option.
Have been looking online for some discount vouchers and have only found 1 active deal from their website which gives 10% off on the total price including vehicle transfer. This is from some Probus membership scheme for which the promo code works online while making the booking but not sure if I will be required to present some form of membership ID at the time of boarding since I am not a member of this club.
Would really appreciate if someone could suggest me a cheaper way to buy the ferry tickets from Sealink. I am looking for tickets or the 2 of us and getting our own car on the ferry as well.
I read somewhere that entertainment book has some voucher codes - would greatly appreciate if someone could please help in finding one or willing to sell or donate their code if they are not planning to use it?
Cheers