Once RNZAF operations consolidated are to Ohakea it will be nigh on impossible, its not the biggest airfield around even with the planned mods, I believe once completed re-establishment of Combat Airwing will be nigh impossible without opening a new base which well just adds to the expense not to mention where to put it... If it was feasible I do ot see why Kiwi pilots could not be put through RAAF trainer school before beginning Aircraft familaristaion training, surely a extra 4-5 pilots are class wouldn't overstretch the RAAF training program, it would only need to be the lead in fighter as the RNZAF still operates there Trainers for the Big birds.
NZ still operates basic fixed wing training capacity, to train pilots for it's fixed and rotary wing based Air Force. The most immediate way to gain a combat capability would be to arm their P-3K's with an appropriate weapon. Harpoon or SLAM-ER would probably be the easiest missiles to integrate.
This would provide significant anti-shipping capacity, with a significant standoff and land attack capability if SLAM-ER were chosen. I cannot imagine a scenario in the South Pacific where a fixed wing, fast jet combat force would be required by NZ.
An armed reconaissance helicopter (such as an armed A-109E Power or armed EC-635) would probably be more useful and FAR less costly in the types of scenario's NZ could be reasonably expected to face in the South Pacific.
It would also have the benefit of likely commonality with the training/light utility helicopter NZ IS tendering for at present and would provide very useful recon and fire support capabilities for the NZ Army, capabilities which are sorely lacking at present. It would also be FAR easier and far quicker to introduce both of these capabilities into NZDF service.
IF funding were found and the politicians could be convinced (probably the BIGGEST hurdle for any such "offensive" capabilities to be introduced int NZDF service) of the need for both projects, they could be implemented very quickly, particularly once the LUH helo is in-service.
If NZ were to become involved in a war further afield, only then would they truly require a fast jet capability. It would be a slow, costly and tedious process however and would have to start with significant infrastructure enhancements and the re-building of corporate knowledge of fast-jet operations within NZDF.
This would probably mean posting a number of RNZAF officers / maintenance personel within foreign militaries to become qualified fast-jet pilots and maintainers and then return to RNZAF once the infrastructure projects (a suitable air base, with maintenance, fuel, logistical, electrical power etc facilities existed) were completed.
The introduction of a fast jet trainer would be the next step, something like the former Air Macchis or Hawk jets for RNZAF to become familiar with operating fast jets again. A fast jet trainer with basic weapons capability like the RAAF Hawk Mk 127's (Mk 82 bombs, 30mm cannon and Sidewinder AAM's) could provide some interim A2G weapons and a basic air intercept capability in the meantime and give back to NZ, SOME ability to control it's airspace.
Once this capability was well established could acquisition of a modern fighter type truly be considered. Second hand options such as ex-USAF or "European" air force F-16's (ex-Netherland for example) would probably provide the greatest "bang for buck". The Netherlands for instance recently offered Chile 16x additional F-16 MLU aircraft for US$160m.
These aircraft are basically of a reasonably advanced F-16C/D standard and are BVR/WVR capable as well as Maverick/LGB/HARM generation weapons capable.
Further MLU upgrades would be needed for them to become "J" series weapons compliant, plus they'd probably need an EWSP and targetting pod capability, upgrade as a minimum.
With the required weapons and sensor package needed for an effective and modern capability, plus acquisition costs of even 16, IF NZ could get the same price (seem to be offered at "mates rates" to Chile because they already purchased 12), NZ would probably still need at least US$500m (NZ$746m) for the intial acquisiton alone. On-going costs would probably double this.
The costs to even get to that stage would probably far exceed this...