chevrolux: Not matter who you are with you will get charged the standard $50. It comes from Chorus. Even in a straight provider churn the $50 fee still prevails.
Examples/proof?
The $50.xx charge is for a standard new copper connection (or at least meant to be as I understand it)
There was a 'churn fee' I believe (unfortunately I can't seem to find proof of this anymore) that was around $25-50, that was charged by Chorus/Telecom Wholesale to recoup Adminministrative costs, INSTEAD of the standard installation charge, this allowed some ISPs like Actrix or Orcon to pass on the benefit by offering reduced length contracts or no contracts if you churned. (Actrix was something like 3 or 6 months instead of 6 or 12 months for a new customer, Orcon churned our broadband+tolls without charge or contract back in 2010/2011-ish).
The only reason I can think of the need for the $50 fee for a customer with ADSL currently, is if they are connected via an ULL exchange and hence on the Vodafone/Orcon/etc networks.