Only option with stock ECU is stock R32 GTR AFMs, you can't run non-standard AFMs on your stock ECU (but Nistune would allow you to), as the stock ECU expects the voltage output of the stock R32 AFMs.
Brand new Nismo GTR AFMs are actually cheaper (about $450 each: http://www.rhdjapan.com/jdm-low/NISMO-Air-...T-AFM-MAF-18459 ), than Brand new Genuine GTR AFMs are (about $530 each: http://www.rhdjapan.com/jdm-low/Nissan-OEM...line-GT-R-58012 ).
The money you save by going with 2x Z32 AFMs (approx $250-300 each), you'll have money left over for Nistune
Other option if you had Nistune is the 80mm green sticker AFMs from GTS-T's (from R33s iirc), I'm sure there's other options too