Sparrow,
As Duck Pilot says, try the Taurama Aquatic centre on Taurama Rd. You can use the gym and/ or the pool. Varying rates for either gym, pool or both for either daily, monthly, etc. Cost are way less than the Airways and it's much better than the Aviat.
I haven't used it for about a year but as I remember the gym isn't airconditioned but there's fans and it was pretty reasonably equipped. The 50m Olympic standard pool wasn't heavily used, mostly expats grinding out laps and a small 20-25m shallow pool that the locals seem to love. Maintenance was starting to get a little dodgy last time I was there though but still OK.