Kiwirail Scenic is offering $99 fares from Christchurch to Wellington (including ferry) and $29 fares from Christchurch to Kaikoura. Sample booking screenshot. The next best price for this fare is $159 so you are saving $60.
For bookings from 12 – 23 August 2015. Travel from 25 September 2015 – 1 May 2016.
Spotted this in today's paper. Note: You need to be using a New Zealand IP address to access this sale so turn off your VPN.
Tempting!!!