The slip came down on State Highway 6 between Haast and Makarora overnight on September 10 and has since caused ongoing disruptions for motorists travelling the major tourism route.
The road is closed every night from 6pm to 8am, and occasionally during daytime hours, particularly in rainy conditions when the slip becomes unstable, or when fog disrupts clearing work.
NZTA senior network manager Mark Pinner said much of the $1.5 million spent on the slip was on the day-to-day operation of the road crew and machines to remove the 50,000 tonnes of rock and debris which had fallen on to the road to date, along with manning two road blocks, communications and having three abseilers on the edge of the slip to spot any movement.
''The amount also includes about $220,000 spent on hiring helicopters for the inspection and sluicing of the slip site during the last six weeks,'' Mr Pinner said.
''At one point, there were three helicopters working at the site, providing a continual sluicing operation.''
It was too early to predict the long-term cost of the slip, he said.
''It will depend on the work needed to stabilise the slip face and on the long-term options to make the road safe and remove the night-time closures.''
NZTA West Coast regional performance manager Pete Connors said last week it was likely to be April or May next year before the slip settled and the road was open all the time, allowing NZTA to implement long-term solutions such as debris fences.
During a series of meetings with affected communities on either side of the slip last week, Mr Connors said the agency had ''no budgetary constraints'' in fixing the slip.
