Depending on where your mate lives, the cheapest way would be do a series of domestic runs at the cheapest fare at the time.

All domestic fares gain a minimum of 8 SPs even if it's a cheap $1 "Grab-a-Seat" fare.
Nightrider $29 Seat only AKL-CHC would be a prime candidate to do a cost-effective status run however, they seemed to be all sold out now.

Otherwise as you said, SP are somewhat tied to actual spend, and depending on route, is around NZ$10 - $15 per SP.

Quick check on Air NZ and it seems they are doing a special to Australia right now, at least for a March search AKL-SYD where Business is ~NZ$1346 return, for 142SP (71SP each way). That's ~NZ$9.48/SP which is pretty good (all things considered).

If the 200 SP required doesn't have to be NZ specific requirement (Elite needs 810 SP to be flown on NZ ticketed/operated flights to re-qual), and if your mate doesn't mind travelling abroad, do some domestic runs in US (with United) or Europe (with SAS) in premium cabins, as they often get you ~NZ$6-NZ$8 per SP.